If he utters someones else's name, that's a pretty good tipoff. Do yourself a favor and don't worry about it. You can't be concerned with what's in his head -- let alone discern or control what he's thinking. Be happy he's having sex with you and not someone else. He isn't cheating if he isn't cheating. And try to fight the jealousy monster a bit better, and try to have more self-respect.