I think it is important to realize that the only person whose emotional and pstchological health you can impact is your own. You can work to make yourself the very best person you can be. You cannot in any way make (or usually even help) someone else be emotionally or psychologically healthy. They have to want it, they have to do all the work to get it, and they have to deal with all those failures along the path to recovery. And even then, there will still be a tendency to find someone unhealthy to be with, if that is the pattern.

You can't be good enough for this girl. And being bad enough for her would be selling your own soul. You can't make her heal, you can't help her heal. The nails are already in this coffin, sticking with her is just going to erode your own self-confidence as she continually throws you over for someone who will mistreat her like she believes she deserves. You need to find someone healthier. Nobody is perfect, but there are plenty of women who don't have any desire or impulse to find abusive mates. Find one of those women for yourself.