Hi Hun- I understand what you are going through. I think that most people will say once a cheater, always a cheater, but I think that works better on a case by case scenario. Maybe this guy really does love you and really does know that he messed up, its hard not to. I think it also depends on what type of relationship he had with this girl. If she was like another long term serious gf, then maybe you have should be a little more concerned about repetition, but if she was a one night, one time thing then its prob not as big a deal. I am a believer than ANY cheating is a huge, massive deal, but I can also appreciate that sometimes things happen. . .Either way, it's probably for the best if you take a little time and decide if being with him is worth the period of stress and accusations and worrying that is to come after something like this. . .Good Luck!