First thing is to leave when you decide to. He says he won't let you leave...will he imprison you by force or kill you? If not, you can leave.
Second thing is what you're going to do about his behaviour.
You can go down the legal route and report it to the police. Gather evidence as much as possible. Document every incident at least. Obtain recordings (audio would be easy, video a bit harder but still possible) if you can.
Or you can go down the illegal route and use violence against him. If you do so, be aware that you must be willing and able to escalate the violence beyond whatever level he is willing to escalate it to. You might not have to (it's possible that a lesser degree of violence from you might be enough to put him off), but you must be willing and able to do so. It's not the sure solution some people are portraying it as being. Also, be aware that it is illegal and you might face legal problems as a result. A conviction for violent crime wouldn't do much for your employment prospects. Finally, it might cause family problems. If, for example, you use a weapon on him and break his arm, how will your parents react? If you are going to go down that route, do use a weapon. You can't half-arse this method and you don't have the skill or strength to try a fair fight, so don't try a fair fight. Attack from surprise, use a weapon. If you're going to use violence, skew the confrontation in your favour as much as possible. A fair fight is for a sporting contest, not for real conflict. It's an ugly method and I wouldn't recommend it. For casual bullying, you might well stop it without inflicting more than a bloody nose and bruising if you've assessed the bully correctly. If you haven't, you'll have made the situation worse. You're not children, so the experience some people have posted about their childhoods is of limited relevance.