Emancipation: Emancipation help

I'm 17, I turn 18 next year. I live with my father and my disabled grandfather, my father is mentally and verbally abusive to me. I'm actually very afraid of him, he says when I turn 18 that I'm not allowed to leave and that if I try to move out he will do whatever he can, including saying that I'm not mentally stable, etc. so I will have to stay with him. He's even threatened that if I move out that he will find me and drag me back. He says that for all the years he's taken care of me that I have to stay because I owe him years that he has wasted, and I cannot live with my mother because my father hasd full custody of me, and she is in prison right now anyway. I'm really afraid of what might happen if I try to move out as soon as I turn 18, and the ways things are going he's driving me insane and I'm always depressed because of him. I'm afraid of telling anyone because I don't want to go into foster care or anything like that. I'm afraid to go and live with my boyfriend or my friend because he knows where they live and I don't know what he would do to me or them. I want out so bad and I feel hopeless. I'm under so much stress because of him. I don't know what to do.