How do you tell if he just wants me for ?

I'm uming you're in middle school. Your boy wants it, all boys do. But he doesn't know what to do with it. He's probably not ready either and the only way he can get some is by macking it out. If he brings the subject up and you tell him you're not ready and he gets mad then leave him. He needs to respect you and if he doesn't then why be with him.