Well, for starters, I think you need to IMMEDIATELY nix him talking about OW to you. You need to tell him that you find it disrespectful, and that he's an adult and you can't control him, but that you will NOT sit and listen to stories about him and his girlfriend (and call her that).
I think that would be an important first step, and a strong boundary, that you could feel very good about enforcing, and it would give you added strength.
