Some men (and women) cheat because there is something lacking in their marriage and the communication skills in that marriage is poor. Some men will cheat because they find it exciting while other men may cheat because they feel their youth is slipping away quickly and they want to feel like other women are still attracted to him. Sometimes getting older is difficult for some individuals. No, it is not easy for a man who has been friends with a female for five years or more; then has an affair (love is about friendship and being lovers,) but sometimes friendship can be mistaken for true love. It's more of an emotional affair between the two when one or both parties are having a difficult time in their life. Considering your husbands ex mistress works at the same company as your husband this makes it even more of a challenge for your husband. If he was caught cheating by you then he either does not want to lose you or, he feels threatened and trapped. If he openly admitted to the affair to you and said it was over then he probably means it. Still, it is possible the affair could still pick up where it left off. It is important that the two of you sit down and communicate each of your feelings without arguing and also seeking marriage counseling to learn the tools to resolve problems in your marriage.