Look I can’t tell you what to do, no one can. Even if I did you might not take the advice. If the guy is still in her life and she doesn’t plan on getting rid of him then most likely she’s not going to be faithful this time around either. The only way to avoid cheating is to kick whoever it is out of their life and to never go back there and try your hardest to be faithful. Even then sometimes it doesnt work. The cheater has to really want to give it up, has to really want to change. Take it from a cheater. It took me years until I was at risk of losing something potentially great. Then one day a person I don’t speak to anymore told me that I didn’t know how to tell the truth unless I was forced to.. and they were right. So I made a change. If she acts like she’s kissing your ass because she’s cheated, most likely she hasn’t changed. But if she really acts like she’s changed, like willing to ditch this guy for you and truly be a better person, then give her a chance.