I have BPD and we think my boyfriend might to because he's experiencing a lot of the symptoms. We both struggle with self sabotaging behaviors. I have in the past cheated in relationships and have had no idea why, and when my partner would find out I'd have a complete break down because I feel like I have no control over myself and get extremely suicidal. I'd honestly not want to hurt the person in the slightest but I would still do it and when thinking about why I couldn't find an answer. It's awful. (I haven't cheated on my current boyfriend). My boyfriend is going through this right now, the only reason I haven't left him is because I understand what it feels like to feel like you are completely out of control, and I recognized exactly how he was feeling in that moment. The issue is we don't know what causes it so how are we supposed to stop it from happening again because just saying "have more self control" is unrealistic for someone who has BPD and has received zero treatment. (Obviously its not certain that he has BPD but if he doesn't then it will be something very similar because what he experiences is almost identical to what I experience). I honestly don't know what to do to help him other than just saying eliminate any all temptation which probably wont be feasible in the long run, and we really need something to help because I cant be in a relationship with someone that constantly cheating on me no matter how much I love them and understand the struggle. 

Also might be relevant info but the known reason for cheating in the past for both of us is liking that kind of attention from others

Sorry if my grammar and formatting isn't great, this is my first reddit post.