I know it would be embarrassing, but are you able to talk to your parents about this? Or perhaps an auntie, trusted teacher or someone? I think it would be helpful to talk it over with someone, and let them help you.

And I do echo what the others say, got to the police, get a lawyer. He should be stopped and I dont think the only other option you have is good. You do not want to date him, end of. Please don't give into him, as whatever goes bad in the future, he will simply blackmail you again. I am sure you could sue him if he did post the pictures, and you need some help to get that message over - to frighten him off.

Good luck, and big hugs.