I like your comment. In long term (normally) older couples I think there may be some of the don't ask, don't tell going on. One or both are straying outside the marital bounds, each probably knows about it - but it is unspoken - because despite articles that scold that the other partner wants to know all bout the discretion, there are many that do not. Why? Because then they would feel compelled to do something about it- and that action is going to shake up their world.

After a certain age or marital longevity when the risk of pregnancy is low, I think there are many couples who just let sleeping dogs lie and don't ask a lot of questions. I live in a community of older people that are pretty upfront that they don't sleep together. That does not equate to behavior, but it seems to be that a lot of older couples (and yes, my spouse and are are older too) that the attitude of cheating seems to take a back seat, relative to remaining together. The issue seems to be less important.