Just remember he did this to you not her, i get misdirecting your anger as I am the gueen of misdirecting, but he is the problem not her. And you did not do anything to cause him to cheat on you, it is not your fault, alot of people have problems in there relationships and they do not cheat.

Good luck, and take care of yourself and your children and remember your children learn from you what is exceptable behaviour in a relationship and when they grow up there choice of relationship types will model yours.