Why haven't you confronted him about his cheating again with this woman? It seems more like you want to know why he did it rather than stop him from doing this. How can you even want to marry a man like this? It won't stop after the two of you walk down the aisle... the problem will still be there until you take a stand. First of all, you need to tell him that this is absolutely unacceptable. Then force him to go to counseling with you. Just taking his word for it that he won't cheat anymore didn't work before, and it won't work now. And you absolutely can not marry this guy!! Don't even set a date or start making wedding plans. In fact, i think you should give him back the ring, and insist that if the two of you work things out, he can propose to you again. Sweety, divorcing him is alot harder than breaking up with him. And if this guy doesn't change, then you need to tell him to hit the road.