All though it's a tough pill to swallow it's his business if he chooses to date if you're separated. It's in very poor taste for him to move too fast, date a friend or friend of a friend or rub it in your face or act as though he's committed to you in a class mandated by the state (I took that class too). It is however your right to tell him to GTFO of this house yesterday and don't let the door hit you in the ass and to keep his private life to himself.
He sounds like a two faced low class jerk and you're better off without him.