Thanks, everyone, for your replies. I am glad to hear of success stories as well as from those who had to draw that line in the sand when things got abusive. No excuse for abuse, by any means. And if someone is not willing to seek help, then there is little that one can do for them. At that point, you need to set boundaries to keep yourself mentally well.

PaintTheRoses88, I'm not sure I was clear - I have two different people in my life with this issue. My sister's bipolar ex, and a friend's new alcoholic husband. My sister's son is in college now, so visitation is no longer an issue. Her ex has long since remarried and moved on, but I guess the situation is still nagging at me. My friend's first husband was abusive, and this may shed some light on her seemingly knee-jerk reaction. I definitely admit that I do not know all the particulars of their situation, and the new husband may be acting irrationally, though I do not think he is being abusive. Some distance may be needed right now, but I am still upset by the rush to call it quits without even trying.

I would love to hear more experiences and opinions on this. to everyone.