You're a doormat. She's a cake eater. She's got you wrapped around her finger and goes off to get her jollies with other men. Is that the life you want to live? Because you're living it. Go ahead and play this as passively as you are and this affair will dig deep roots and make it almost impossible for you to fix your marriage. You can't fix a marriage that has more than two people in it. Nobody respects a doormat.