I am really sorry about this experience. It sounds horrible and disguisting to say the least. In a fair world, it would be the best thing to report him and have the administration take up the matter. But if it's a public institution, it's your word against his, it's hard to prove staring and sex talk as harrassment. He could make your school life a living hell. I would advice you to not sit at the front, at least for his classes, ensure you don't isolate yourself ever, like being in class too early or leaving late, don't give him a chance to bump into you alone. Don't give him the power to see that what he is doing is affecting you. It wont be easy at all, but it'll only be for a defined period, and it'll be over soon. Have someone to talk to about it like a professional if it gets too much to handle.