My brother plays this game all of the time. It is one game that I've kept my husband away from
In all seriousness, though, you need to set some boundaries. From what I know, it's a very addictive game. Set some times where he IS allowed to play the game, rather than focusing on when he CAN'T play the game. For instance, if your favorite show is on Tuesday nights at 7, give him from 6-8 to play on Tuesdays. This will keep him out of your hair and give him time he needs alone.
All relationships require both parties to have some "alone" time. We all need it. This is his release and what he likes to do when he's alone. It's not fair to take it away completely. He doesn't control what you do, so you can't control what he does. Make it so that it fits in with what you will accept. If he chooses not to compromise with you, take things from there.
As far as "cheating" with other women in the game, I would have to say that I doubt that there's much real communication going on there. True WoW players are not really getting to know each other, they're just playing the game. Truly, I would be surprised to find out that people were creating meaningful relationships while playing the game. If he's talking with them outside of the game, however, you might want to talk to him about that.
Bottom line, you need to talk to him about all of this. Tell him how it makes YOU feel. Use "I" statements: "I don't like when..." "I feel hurt when..." The less you accuse him, the more he'll listen. Talk to him about your feelings.