Being on the young end at this forum AND very new, I apologize ahead of time for any naivety. ((And I think I just point that out cause galagirl has provided with such a great breakdown as it is.. XD))
Honestly it does not sound like you want to be with him anymore. Or at least you are just willing to be unhappy in a relationship with him.
It seems your emotions are not very flexible concerning your monogamy with him. You have to ask yourself, is it worth suffering to stay with him? Do you want to stay with him so bad that you don't mind letting yourself hurt, is it because you believe one day you heal and feel you can ((learn/heal)) to be happy in a monogamous relationship? Perhaps you just need the forum to vent your feelings, which is perfectly all right I think. Maybe deep down you believe that you can be happy again, but with just your husband. It seems that way cause you haven't chosen to leave your husband(and that could rely on a whole bag of other issues that have nothing to do with your desired relationship dynamic.) I guess what I'm trying to get at is, you are hurting, and it may help to dig down a bit deeper as to why you currently hurt, find out if you're going to continue to hurt, and if it's worth it. Being unhealthy to yourself, trying to convince yourself of something you might not ever agree with will be your undoing, and I don't mean just cheating on your husband.