My bi-polar fiance (ex, that is), had an affair just a few weeks after asking me to marry him. I'm like the rest of you. It's so hard and so painful to try to imagine the thought process that makes someone do that. He was diagnosed and took medication for a little while a few years ago but he soon made excuses not to take the meds. He won't get help and he has had several affairs in the five years we've been together. But even after cheating on me after the engagement I was willing to try to work on things again if he would try. He just wasn't willing. He says he's empty inside and doesn't feel anything. Maybe it's the depressive state. I don't know. I don't know if he's going to cycle back and want to get back together when he's feeling good, or if this is really the end. But I feel like I need to try to move on, at least until he starts trying to really help himself. He knows what his problem is and I think he should start taking some responsibility for it. He won't listen to me anyway. I don't know if this helps, but that's been my experience with a bi-polar person who's had affairs. Good luck to you. I know how awful it is. I'll say a prayer for you.