good morning boo,
i really do feel for you. i hate that you are going through this. i wish no one ever had to be cheated on. the blow to the gut made me sick. i don't think i ate for 6 weeks.
i found it really helpful to stay in reality as best i could since what i thought had been my life was really a bunch of lies. things seemed so confusing to me. i would not put much stock in anything he says right now, including the girlfriend stuff. he is busted and wants to appease you. he might agree to your terms right now, but there really isn't any substance behind it. he has to change (words not actions) on his own independent of you and anything you force him to do. otherwise it is just more confusion thrown into the mix. more lies that he is doing the right things that you want him to do. that leads to more hurt later when he doesn't follow through.
also, i know you don't give a crap about her. but, part of staying in reality means seeing what's what. your husband is the liar and cheat, not that other woman. he lied to and cheated on her too. of course your pain in greater, but it doesn't sound like she was at fault. it sounds like you found info that there were other women as well. husband created bogus facebook and email accounts to correspond with women. what a psycho pervert.
i might resist the urge to rationalize his deceit by analyzing how he was unhappy or that sex wasn't happening with you two. he is a liar, not you. there is nothing you did or didn't do to deserve him cheating on you. if he was unhappy, then he should have left. he didn't, chose to cheat instead. coward too. that is all about him and his messed up way of dealing with life. kind of like his alcoholism. selfishness, immaturity and all about him.
i hate this for you. but having been in your shoes, taking some time away from him to think might be really good and helpful for you. can you or he leave the house today and go home?