James:

It may seem contradictory to the idea of being "nice," but Nice People sometimes act out their issues by having affairs. Anger and hurt are quite understandable responses to such a destructive act. It would probably be tremendously helpful for both of you to understand the role that anxious attachment played in the affair, though this should never be used as an excuse for what’s been done. Ultimately, the chronically nice person has to be able to accept responsibility for their choices and take initiative to clean up messes and create an environment of love and growth. Forgiveness is an important step of reconciliation, but it doesn’t make the other person trustworthy. That’s something they have to achieve on their own.