You said,she said, "since she had an affair on him this would even them out."
I would be leerie of her friendship, it's almost like she's using you to relieve her own guilt of her affair.
A good friend wouldn't do that, almost sounds like some twisted game.
I'm glad you didn't become part of that game, sounds like you have enough stuff in your life going on, and you certainly do not need to be involved with such games.
I wish you lots of luck, and are able to persue the things you want in life that will enable you to have independence from all of this, even start over, you are young and still have a future.
Please take care of yourself,your mind,health and your children.