It appears that all studies report that men’s porn use is linked to poorer sexual and relationship satisfaction. Some of these studies are longitudinal, thus implying causation. One study demonstrates causation as it had participants eliminate porn use for a period of time:

Pornography Consumption and Satisfaction: A Meta-Analysis (2017) -
EXCERPT: However, pornography consumption was associated with lower interpersonal satisfaction outcomes in cross-sectional surveys, longitudinal surveys, and experiments. Associations between pornography consumption and reduced interpersonal satisfaction outcomes were not moderated by their year of release or their publication status. But analyses by sex indicted significant results for men only.

Does Viewing Pornography Reduce Marital Quality Over Time? Evidence from Longitudinal Data (2016) -
EXCERPT: This study is the first to draw on nationally representative, longitudinal data (2006-2012 Portraits of American Life Study) to test whether more frequent pornography use influences marital quality later on and whether this effect is moderated by gender. In general, married persons who more frequently viewed pornography in 2006 reported significantly lower levels of marital quality in 2012, net of controls for earlier marital quality and relevant correlates. Pornography's effect was not simply a proxy for dissatisfaction with sex life or marital decision-making in 2006. In terms of substantive influence, frequency of pornography use in 2006 was the second strongest predictor of marital quality in 2012

Till Porn Do Us Part? Longitudinal Effects of Pornography Use on Divorce (2017) -
EXCERPT: Beginning pornography use between survey waves nearly doubled one's likelihood of being divorced by the next survey period, from 6 percent to 11 percent, and nearly tripled it for women, from 6 percent to 16 percent. Our results suggest that viewing pornography, under certain social conditions, may have negative effects on marital stability.

Pornography and Marriage (2014) -
EXCERPT: We used data on 20,000 ever-married adults in the General Social Survey to examine the relationship between watching pornographic films and various measures of marital well-being. We found that adults who had watched an X-rated movie in the past year were more likely to be divorced, more likely to have had an extramarital affair, and less likely to report being happy with their marriage or happy overall. We also found that, for men, pornography use reduced the positive relationship between frequency of sex and happiness. Finally, we found that the negative relationship between pornography use and marital well-being has, if anything, grown stronger over time, during a period in which pornography has become both more explicit and more easily available.

Are Pornography Users More Likely to Experience A Romantic Breakup? Evidence from Longitudinal Data (2017) -
EXCERPT: This study examined whether Americans who use pornography, either at all or more frequently, are more prone to report experiencing a romantic breakup over time. Longitudinal data were taken from the 2006 and 2012 waves of the nationally representative Portraits of American Life Study. Binary logistic regression analyses demonstrated that Americans who viewed pornography at all in 2006 were nearly twice as likely as those who never viewed pornography to report experiencing a romantic breakup by 2012, even after controlling for relevant factors such as 2006 relationship status and other sociodemographic correlates. This association was considerably stronger for men than for women and for unmarried Americans than for married Americans. Analyses also showed a linear relationship between how frequently Americans viewed pornography in 2006 and their odds of experiencing a breakup by 2012.

From Bad to Worse? Pornography Consumption, Spousal Religiosity, Gender, and Marital Quality (2016) -
EXCERPT: I test the above hypotheses using data from Wave 1 of the Portraits of American Life Study (PALS), which was fielded in 2006. PALS is a nationally representative panel survey with questions focusing on a variety of topics....Looking at bivariate correlations, for the full sample, viewing pornography is negatively associated with overall marital satisfaction, suggesting that those who view pornography more often tend to be less satisfied in their marriage than those who view pornography less often or never

Internet pornography and relationship quality: A longitudinal study of within and between partner effects of adjustment, sexual satisfaction and sexually explicit internet material among newly-weds (2015) -
EXCERPT: The data from a considerable sample of newlyweds showed that SEIM use has more negative than positive consequences for husbands and wives. Importantly, husbands’ adjustment decreased SEIM use over time and SEIM use decreased adjustment. Furthermore, more sexual satisfaction in husbands predicted a decrease in their wives’ SEIM use one year later, while wives’ SEIM use did not change their husbands’ sexual satisfaction

Explicit Sexual Movie Viewing in the United States According to Selected Marriage and Lifestyle, Work and Financial, Religion and Political Factors (2017)
EXCERPT: Analyses involved 11,372 adults who responded to questions about demographics and explicitly sexual movie use in the General Social Survey (GSS) from 2000 to 2014. Viewing such movies was related to less happiness in marriage, multiple sex partners in past year, less satisfaction with one’s financial situation, no religious preference, and a more liberal political orientation. Explicit sexual movie viewing is associated with factors from diverse domains, including poorer relationship quality, more liberal sexual views and practices, poorer economic conditions, lower religious orientation or commitment, and more liberal political views.

More than a dalliance? Pornography consumption and extramarital sex attitudes among married U.S. adults (2014) -
EXCERPT: This brief report used national panel data gathered from two separate samples of married U.S. adults. Data were gathered from the first sample in 2006 and in 2008. Data were gathered from the second sample in 2008 and in 2010. Consistent with a social learning perspective on media, prior pornography consumption was correlated with more positive subsequent extramarital sex attitudes in both samples, even after controlling for earlier extramarital sex attitudes and nine additional potential confounds. In total, the results of the present study are consistent with the theoretical premise that pornography consumption leads to the acquisition and activation of sexual scripts, which are then used by many consumers to inform their sexual attitudes (Wright, 2013a; Wright et al., 2012a)

Associations between young adults’ use of sexually explicit materials and their sexual preferences, behaviors, and satisfaction (2011) –
EXCERPT: Higher frequencies of sexual explicit material (SEM) use were associated with less sexual and relationship satisfaction. The frequency of SEM use and number of SEM types viewed were both associated with higher sexual preferences for the types of sexual practices typically presented in SEM. These findings suggest that SEM use can play a significant role in a variety of aspects of young adults' sexual development processes.

Pornography’s Impact on Sexual Satisfaction (1988) -
EXCERPT: Male and female students and nonstudents were exposed to videotapes featuring common, nonviolent pornography or innocuous content. Exposure was in hourly sessions in six consecutive weeks. In the seventh week, subjects participated in an ostensibly unrelated study on societal institutions and personal gratifications. [Porn use] strongly impacted self-assessment of sexual experience. After consumption of pornography, subjects reported less satisfaction with their intimate partners—specifically, with these partners' affection, physical appearance, sexual curiosity, and sexual performance proper. In addition, subjects assigned increased importance to sex without emotional involvement. These effects were uniform across gender and populations.

Adolescents’ Exposure to Sexually Explicit Internet Material and Sexual Satisfaction: A Longitudinal Study (2009) -
EXCERPT: Between May 2006 and May 2007, we conducted a three-wave panel survey among 1,052 Dutch adolescents aged 13–20. Structural equation modeling revealed that exposure to SEIM consistently reduced adolescents’ sexual satisfaction. Lower sexual satisfaction (in Wave 2) also increased the use of SEIM (in Wave 3). The effect of exposure to SEIM on sexual satisfaction did not differ among male and female adolescents.

Individuals who never viewed SEM reported higher relationship quality on all indices than those who viewed SEM alone (2011) –
EXCERPT: As expected, individuals who did not view SEM (sexually explicit material) at all reported lower negative communication and higher dedication than individuals who viewed SEM alone or both alone and with their partner.

Sexual media use and relational satisfaction in heterosexual couples (2010)
EXCERPT: Results revealed that a higher frequency of men's sexual media use related to negative satisfaction in men

Young Adult Women’s Reports of Their Male Romantic Partner’s Pornography Use as a Correlate of Their Self-Esteem, Relationship Quality, and Sexual Satisfaction (2012) -
EXCERPT: The purpose of this study was to examine the relationships between men’s pornography use, both frequency and problematic use, on their heterosexual female partner’s psychological and relational well-being among 308 young adult college women. Results revealed women’s reports of their male partner’s frequency of pornography use were negatively associated with their relationship quality. More perceptions of problematic use of pornography was negatively correlated with self-esteem, relationship quality, and sexual satisfaction.

Korean Men’s Pornography use, Their Interest in Extreme Pornography, and Dyadic Sexual Relationships (2014) -
EXCERPT: Six-hundred eighty-five heterosexual South Korean male college students participated in an online survey. The majority (84.5%) of respondents had viewed pornography, and for those who were sexually active (470 respondents), we found that higher interest in degrading or extreme pornography was associated with the experience of role-playing sexual scenes from pornography with a partner, and a preference for using pornography to achieve and maintain sexual excitement over having sex with a partner.

Pornography and the Male Sexual Script: An Analysis of Consumption and Sexual Relations (2014) -
EXCERPT: We argue pornography creates a sexual script that then guides sexual experiences. To test this, we surveyed 487 college men (ages 18-29 years) in the United States to compare their rate of pornography use with sexual preferences and concerns. Results showed the more pornography a man watches, the more likely he was to use it during sex, request particular pornographic sex acts of his partner, deliberately conjure images of pornography during sex to maintain arousal, and have concerns over his own sexual performance and body image. Further, higher pornography use was negatively associated with enjoying sexually intimate behaviors with a partner.

Adult Social Bonds and Use of Internet Pornography (2004)
EXCERPT:Complete data on 531 Internet users are taken from the General Social Surveys for 2000. Social bonds measures include religious, marital, and political ties. Measures of participation in sexual and drug-related deviant lifestyles, and demographic controls are included. The results of a logistic regression analysis found that among the strongest predictors of use of cyberporn were weak ties to religion and lack of a happy marriage.

A Common-Fate Analysis of Pornography Acceptance, Use, and Sexual Satisfaction Among Heterosexual Married Couples (2016) -
EXCERPT: Results indicated that the shared variance of pornography acceptance was positively associated with both spouses' pornography use and that spouses' pornography use was negatively associated with their own sexual satisfaction. Wives' pornography use was found to be positively associated with the couple's shared variance of sexual satisfaction, but pornography use did not significantly mediate the relationship between pornography acceptance and sexual satisfaction.

Differences in Pornography Use Among Couples: Associations with Satisfaction, Stability, and Relationship Processes (2016) -
EXCERPT: The present study utilized a sample of 1755 adult couples in heterosexual romantic relationships to examine how different patterns of pornography use between romantic partners may be associated with relationship outcomes. While pornography use has been generally associated with some negative and some positive couple outcomes, no study has yet explored how differences between partners may uniquely be associated with relationship well-being. Results suggested that greater discrepancies between partners in pornography use were related to less relationship satisfaction, less stability, less positive communication, and more relational aggression. Mediation analyses suggested that greater pornography use discrepancies were primarily associated with elevated levels of male relational aggression, lower female sexual desire, and less positive communication for both partners which then predicted lower relational satisfaction and stability for both partners.

Factors Predicting Cybersex Use and Difficulties in Forming Intimate Relationships among Male and Female Users of Cybersex (2015) -
EXCERPT:This study used the Cybersex addiction test, Craving for pornography questionnaire, and a Questionnaire on intimacy among 267 participants (192 males and 75 females) mean age for males 28 and for females 25, who were recruited from special sites that are dedicated to pornography and cybersex on the Internet. Results of regression analysis indicated that pornography, gender, and cybersex significantly predicted difficulties in intimacy and it accounted for 66.1% of the variance of rating on the intimacy questionnaire. Second, regression analysis also indicated that craving for pornography, gender, and difficulties in forming intimate relationships significantly predicted frequency of cybersex use and it accounted for 83.7% of the variance in ratings of cybersex use.

Pornography use: who uses it and how it is associated with couple outcomes (2013) -
EXCERPT: This study examined associations among pornography use, the meaning people attach to its use, sexual quality, and relationship satisfaction. Participants were couples (N = 617 couples) who were either married or cohabiting at the time the data were gathered. Overall results from this study indicated substantial gender differences in terms of use profiles, as well as pornography's association with relationship factors. Specifically, male pornography use was negatively associated with both male and female sexual quality, whereas female pornography use was positively associated with female sexual quality.

A Love That Doesn’t Last: Pornography Consumption and Weakened Commitment to One’s Romantic Partner (2012) -
EXCERPT: Study 1 found that higher pornography consumption was related to lower commitment Study 3 participants were randomly assigned to either refrain from viewing pornography or to a self-control task. Those who continued using pornography reported lower levels of commitment than control participants. Study 5 found that pornography consumption was positively related to infidelity and this association was mediated by commitment. Overall, a consistent pattern of results was found using a variety of approaches including cross-sectional (Study 1), observational (Study 2), experimental (Study 3), and behavioral (Studies 4 and 5) data.

Male Partners’ Perceived Pornography Use and Women’s Relational and Psychological Health: The Roles of Trust, Attitudes, and Investment (2015) - EXCERPT: Results revealed that women’s reports of their male partners’ pornography use were related to less relationship satisfaction and more psychological distress. These findings indicated that when male partners’ perceived pornography use is high, women who have low or mean levels of relationship investment have less relationship trust. Finally, our results revealed that the relationship between male partners’ perceived pornography use and relational and psychological outcomes exist regardless of women’s own attitudes toward pornography

Relationship of love and marital satisfaction with pornography among married university students in Birjand, Iran (2015) -
EXCERPT:This descriptive-correlation study was conducted on 310 married students studying at private and public universities in Birjand, in 2012-2013 academic year using random quota sampling method. It appears that pornography has a negative impact on love and marital satisfaction.

Sexual media use and relational satisfaction in heterosexual couples (2011) -
EXCERPT: This study assessed how sexual media use by one or both members of a romantic dyad relates to relationship and sexual satisfaction. A total of 217 heterosexual couples completed an Internet survey that assessed sexual media use, relationship and sexual satisfaction, and demographic variables. Results revealed that a higher frequency of men's sexual media use related to negative satisfaction in men, while a higher frequency of women's sexual media use related to positive satisfaction in male partners. Reasons for sexual media use differed by gender

Wives' Experience of Husbands' Pornography Use and Concomitant Deception as an Attachment Threat in the Adult Pair-Bond Relationship (2009) -
EXCERPT: Evidence is growing that pornography use can negatively impact attachment trust in the adult pair-bond relationship. Analyses uncovered three attachment-related impacts from husbands' pornography use and deception: (1) the development of an attachment fault line in the relationship, stemming from perceived attachment infidelity; (2) followed by a widening attachment rift arising from wives' sense of distance and disconnection from their husbands; (3) culminating in attachment estrangement from a sense of being emotionally and psychologically unsafe in the relationship. Overall, wives reported global mistrust indicative of attachment breakdown.

Men’s leisure and women’s lives: The impact of pornography on women (1999)
EXCERPT: The section of the interview where the women discussed their own current or past relationships with men revealed additional insight into the effect of pornography on such relationships. Fifteen of the women were in, or had been in, relationships with men who rented or bought pornography at least on an occasional basis. Of these 15 women, four expressed strong dislike of their husband’s or partner’s leisure time interest in pornography. It was clear that the husbands’ use of pornography affected the wives’ feeling about themselves, their sexual feelings, and their marital relationships in general

Exploring actor and partner correlates of sexual satisfaction among married couples (2010) -
EXCERPT: Using the Interpersonal Exchange Model of Sexual Satisfaction, we consider how infidelity, pornography consumption, marital satisfaction, sexual frequency, premarital sex, and cohabitation are associated with married couples’ sexual satisfaction. Data from 433 couples are analyzed with structural equation models to determine the contributions. Finally, some evidence suggests that pornography consumption is costly for own and spouse’s sexual satisfaction, especially when pornography is used by only one spouse.

Sexually explicit media use and relationship satisfaction a moderating role of emotional intimacy? (2016) -
EXCERPT: For both men and women, significant, yet modest negative zero-order correlations between SEM use and relationship satisfaction were found, indicating that increased SEM use was associated with lower relationship satisfaction across gender.

Sex in America Online: An Exploration of Sex, Marital Status, and Sexual Identity in Internet Sex Seeking and Its Impacts (2008) -
EXCERPT: This was an exploratory study of sex and relationship seeking on the Internet, based on a survey of 15,246 respondents in the United States Seventy-five percent of men and 41% of women had intentionally viewed or downloaded porn. A symmetrical relationship was revealed between men and women as a result of viewing pornography, with women reporting more negative consequences, including lowered body image, partner critical of their body, increased pressure to perform acts seen in pornographic films, and less actual sex, while men reported being more critical of their partners' body and less interested in actual sex.

Effect of soft core pornography on female sexuality (2016) -
EXCERPT: An overall 51.6% of participants who were aware that their husbands were positive watchers reported experiencing negative emotions (depression, jealous), whereas 77% reported changes in their husbands’ attitude. Non-watchers watchers were more satisfied with their sexual life compared with their counterparts. Although watching soft-core pornography had a statistically significant effect on sexual desire, vaginal lubrication, ability to reach orgasm, and masturbation, it had no statistically significant effect on coital frequency. Watching soft-core pornography affects female sexual life by increasing sexual boredom in both men and women, causing relational difficulties.

Internet Pornography Consumption and Relationship Commitment of Filipino Married Individuals (2016) -
EXCERPT: Internet pornography has many adverse effects, especially to the relationship commitment. The use of pornography directly correlates to a decrease in sexual intimacy. Hence, this might lead to weakening of the relationship of their partner. To find out the relevance of the claim, the researchers aimed to explore the relationship of Internet pornography consumption to the relationship commitment of married individuals in the Philippines. It is revealed that Internet pornography consumption has an adverse effect on the relationship commitment of married Filipino couples. Furthermore, watching porn online weakened the relationship commitment that leads to an unstable relationship. This investigation found out that internet pornography consumption has a nominal negative effect on the relationship commitment of Filipino married individuals.

Perceptions of relationship satisfaction and addictive behavior: Comparing pornography and marijuana use (2016) -
EXCERPT: This study examined if negative outcomes due to a romantic partner’s excessive pornography use are different than negative outcomes produced by other compulsive or addictive behaviors, specifically marijuana use. This study suggests that problematic partner pornography use and problematic partner marijuana use are perceived to similarly impact romantic relationships and contribute to a decrease in relationship satisfaction.

Psychological, Relational, and Sexual Correlates of Pornography Use on Young Adult Heterosexual Men in Romantic Relationships (2014) -
EXCERPT: Thus, the purpose of this study was to examine theorized antecedents (i.e., gender role conflict and attachment styles) and consequences (i.e., poorer relationship quality and sexual satisfaction) of men's pornography use among 373 young adult heterosexual men. Findings revealed that both frequency of pornography use and problematic pornography use were related to greater gender role conflict, more avoidant and anxious attachment styles, poorer relationship quality, and less sexual satisfaction.

Associations between relational sexual behaviour, pornography use, and pornography acceptance among US college students (2014) -
EXCERPT: Using a sample of 792 emerging adults, the present study explored how the combined examination of pornography use, acceptance, and sexual behaviour within a relationship might offer insight into emerging adults' development. High male pornography use tended to be associated with high engagement in sex within a relationship and was associated with elevated risk-taking behaviours. High female pornography use was not associated with engagement in sexual behaviours within a relationship and was general associated with negative mental health outcomes.

The effects of sexually explicit material use on romantic relationship dynamics (2016) -
EXCERPT: More specifically, couples, where no one used, reported more relationship satisfaction than those couples that had individual users. This is consistent with the previous research demonstrating that the solitary use of sexually explicit material results in negative consequences. With gender effects held constant, individual users reported significantly less intimacy and commitment in their relationships than non-users and shared users. Our study found that high frequency users are more likely to have lower relationship satisfaction and intimacy in their romantic relationships.

Viewing Sexually-Explicit Materials Alone or Together: Associations with Relationship Quality (2011) -
EXCERPT: This study investigated associations between viewing sexually-explicit material (SEM) and relationship functioning in a random sample of 1291 unmarried individuals in romantic relationships. Individuals who never viewed SEM reported higher relationship quality on all indices than those who viewed SEM alone. The only difference between those who never viewed SEM and those who viewed it only with their partners was that those who never viewed it had lower rates of infidelity.

Cyberpornography: Time Use, Perceived Addiction, Sexual Functioning, and Sexual Satisfaction (2016) -
EXCERPT: First, even when controlling for perceived addiction to cyberpornography and overall sexual functioning, cyberpornography use remained directly associated with sexual dissatisfaction. Even though this negative direct association was of small magnitude, time spent viewing cyberpornography seems to be a robust predictor of lower sexual satisfaction.Our results highlight that psychosexual outcomes are similar for men and women. Thus, we observed negative psychosexual functioning in both women and men.

Internet Pornography Exposure and Women's Attitude Towards Extramarital Sex: An Exploratory Study (2013) -
EXCERPT: This exploratory study assessed the association between adult U.S. women's exposure to Internet pornography and attitude towards extramarital sex using data provided by the General Social Survey (GSS). A positive association between Internet pornography viewing and more positive extramarital sex attitudes was found.

Pornography sexual socialization and satisfaction among young men (2010) -
EXCERPT: An on-line survey dataset that included 650 young Croatian men aged 18-25 years was used to explore empirically the model. Structural equation analyses suggested that negative effects of early exposure to SEM on young men's sexual satisfaction could be stronger than positive effects.

Influence of popular erotica on judgments of strangers and mates (1989) -
EXCERPT: In Experiment 2, male and female subjects were exposed to opposite sex erotica. In the second study, there was an interaction of subject sex with stimulus condition upon sexual attraction ratings. Decremental effects of centerfold exposure were found only for male subjects exposed to female nudes. Males who found the Playboy-type centerfolds more pleasant rated themselves as less in love with their wives.

Effects of Prolonged Consumption of Pornography on Family Values (1988) -
EXCERPT: Male and female students and nonstudents were exposed to videotapes featuring common, nonviolent pornography or innocuous content. Exposure lowered the evaluation of marriage, making this institution appear less significant and less viable in the future. Exposure also reduced the desire to have children and promoted the acceptance of male dominance and female servitude. With few exceptions, these effects were uniform for male and female respondents as well as for students and nonstudents.

The Role of Internet Pornography Use and Cyber Infidelity in the Associations between Personality, Attachment, and Couple and Sexual Satisfaction (2017) -
EXCERPT: Our results indicated that pornography use is associated with couple and sexual difficulties through increased cyber infidelity. Pornography use was negatively related to sexual satisfaction for men, but positively for women. In men, pornography use is associated with higher sexual desire, stimulation, and gratification. However, these effects may lead to decreased sexual desire their partner and decreased sexual satisfaction within the couple.

Relationship quality predicts online sexual activities among Chinese heterosexual men and women in committed relationships (2016) -
EXCERPT: As predicted, individuals with lower relationship quality in real life, including low relationship satisfaction, insecure attachment, and negative communication patterns, engaged in OSAs more frequently. Overall, our results suggest that variables influencing offline infidelity may also influence online infidelity.

Associative pathways between pornography consumption and reduced sexual satisfaction (2017) -
EXCERPT: Pornography consumption frequency was associated with perceiving pornography as a primary source of sexual information, which was associated with a preference for pornographic over partnered sexual excitement and the devaluation of sexual communication. Preferring pornographic to partnered sexual excitement and devaluing sexual communication were both associated with less sexual satisfaction.

Effect of Erotica on Young Men's Aesthetic Perception of Their Female Sexual Partners (1984) -
EXCERPT: Male undergraduates were exposed to (a) nature scenes or (b) beautiful versus (c) unattractive females in sexually enticing situations. Thereafter, they assessed their girl friends' sexual appeal and evaluated their satisfaction with their mates. On pictorial measures of bodily appeal profiles of flat through hypervoluptuous breast and buttock, preexposure to beautiful females tended to suppress mates' appeal, while preexposure to unattractive females tended to enhance it. After exposure to beautiful females, mates' aesthetic value fell significantly below assessments made after exposure to unattractive females; this value assumed an intermediate position after control exposure.

The pervasive role of sex mindset: Beliefs about the malleability of sexual life is linked to higher levels of relationship satisfaction and sexual satisfaction and lower levels of problematic pornography use (2017) -
EXCERPT: The examined model showed that growth sex mindset had moderate positive association with sexual satisfaction and relationship satisfaction while problematic pornography use only showed a negative, but weak one.