So, I have two friends in a relationship. I found out that recently Domonique (formerly B) (who is bipolar) punched and slapped Frances (formerly A). I was obviously upset but while trying to let Frances know that regardless of illness Domonique's behavior was not ok. Then Frances told me Domonique would never do it again, they were sure, and also that Frances had slapped Domo once years ago and thus knows how frustrated Domo must have felt before it happened and how awful Domoniqe feels about it now. I am confused as to what to do or say or feel.

I care about them both, but I'm concerned. From what I have observed before this incident, Frances is unlikely to leave and Domonique is likely to hit again. But Frances's admission about the past is...troubling, to say the least.

Do you really think if a person hits someone once it's destined to happen again unless that person gets serious professional help? This is what I've been taught, but...I dunno. I've known people who have admitted they once hit a spouse in an argument, but felt remorseful and shitty and never did it again. I've also known people who have been the victims of abuse and say "The abuse will continue. It never happens just once." And I know it isn't quite the same thing, but my brief "fling" with my rapist involved me using a lot of the same excuses spousal abuse victims say when he would hurt me or publicly humiliate me.

So IDK...advice please??? Do mutually abusive hetero relationships actually exist, and what can a concerned outsider do?