What does this Text mean??

It means that he has a girlfriend, but he's possibly interested in cheating on her with you. Because he probably thinks you're slutty, even if you're not, since you showed him your at a party. If you really don't want his girlfriend to go through what you did then stop talking to him. He probably knows he's hot and and knows that he can get away with having more than one girl. Otherwise he's just going to play games with you, and her and see what he can get away with.