As others have said, you really need to talk to him. You may find the best thing for both of you is to have a close friendship rather than a relationship. It's absolutely fine for you to not want sex, and you don't have to have it, but it's likely to mean you don't have a partner either. I can see why he keeps making moves - he won't realise that he's scaring you and he's hoping to seduce you. Unless you explain you are not comfortable with sex or sexual advances, he won't know, and will continue to do it. He's probably feeling rejected and confused and doesn't know why you're having less sex with him. You must explain how you're feeling to him.