Dump her.
You have no committment to her and she has proven she is trash. Move on. I'm sure your situation is probably not like mine but I'm not so sure that taking the high road is always the best.
My ex cheated on me one, and I took him back after he assured me he would go to counseling. I took the high road and said very little about what was going on to anyone other than the closest immediate family. Because of this he was able to hide a great many of his mental health issues with his friends and coworkers, and continued to get support for the behaviors which are so destructive for him and he never went through with the counseling and started cheating again.
When I found out the second time, I dumped and subsequently divorced him. I now am very clear and honest about what the issues were at the time of the divorce and continue to be very frank and specific about the situation, when approached by anyone. I name names, I name the specific disorders and if need be I pull out supporting records. He absolutely hates this, because he can no longer hide behind his good guy image and project his problems onto me or others and manipulate us as he has in the past. It did have a some benefit - because he now on medication and seeing a therapist.
Granted my ex is a psycho - his words, not mine. But I found that simply taking the high road isn't always the best thing to do. Sometimes honesty is the best approach.
Good luck!