If he was so wonderful he would not be cheating on his wife and 2 y.o.!!! I think somewhere deep inside, you know it's a bad idea, otherwise you wouldn't have posted the question. If you choose to stay with him (which can only lead to heartbreak) make him use a condom!!!!! Don't take the risk. If he's cheating on his wife, chances are he's cheating on you (regardless of what he says). Obviously I don't know you personally, but you (as do all women) deserve better than this guy is giving you. You say you don't want to lose him, but face it you've never had him! Walk away now while you still have your dignity and health (who knows how many other people he has had unprotected sex with!). If you can't walk away now....protect yourself (MAKE HIM WEAR A CONDOM, IF HE REFUSES...REFUSE TO HAVE SEX WITH HIM) and the future partner(s) (who will cherish and truly care for you) that you will undoubtedly have when you are finally able to walk away from him. Take care of yourself.