Well, it’s a pretty interesting situation you’ve got there. And the reason he treats you like so could vary.
-He may enjoy the title of boyfriend…having a girlfriend, being in a relationship, it just sounds good to him. It is an ego booster for him
-Sex. I’m not sure if you guys participate in sexual activities but if you do he could be using you to recieve that
-He doesn’t want to lose you. He doesn’t get anything out of the relationship anymore. It could mean less to him. But, he’s still holding on because somewhere in him…he really does need you. And the thought of not having you is scarier than the thought of being in a bad relationship
Hope that was some help!