Why is he so hostile?

Sounds like a lot of dishonesty between you and him, on both parts. He probably got his feelings hurt, when you rejected him, and he's having a hard time being just your friend. This is common. If you two aren't getting along, just leave him alone. I think he's being hostile because he liked you, and he would still probably go out with you, and he's not smart enough to realize he should just move on. It obviously sounds like he doesn't enjoy being just your friend, but he probably is thinking he might have a chance with you some day. It just sounds too complicated, if he's a jerk to you just step aside, don't give into him.