In your opinion, am I being way too fair to my husband's mistress?

He still committed to you when you got married. I think the fact that he's on the fence on this one probably gives you a good idea about the kind of man he's become. You made mistakes, we've all made mistakes. We've all been mean and selfish. However, at this point in your life, you need to figure out what's best for you and your children. Personally, I think that you deserve something better than what you're husband is giving you. That being said, find a better husband, provider, friend, lover, etc.