Have learned this myself when interacting with those who have BPD. I used to take it personally that everything I did, no matter how fair I was to them, always ended with me being the "bad guy" anyway. It hurts a little that someone cannot trust you no matter how much effort you put into earning their trust. That's why understanding BPD is important, as it provides context. All you can really do is say what you mean, mean what you say, be consistent with your own behavior around them, and not take their paranoia so close to heart that you're completely put off from interacting with them, 'cause by then they really will feel deserted.