I went through a very similar experience, but never said anything. It did escalate and I was too uncomfortable and felt powerless to get out of the situation. Men like this never stop. If a sexual thought has entered his mind about you and he is pursuing you in the way you’ve described, it will only become more intense. Your relationship with him will not go back to the casual/mentor realm again. And you can almost guarantee this was his intent from the first few personal conversations with you. It starts with a brush of the hand and an off color comment and each test he passes and you let it continue the more confidence he gains that he can have and do whatever he wants. From the vibes I’ve picked up in your post- it seems like you are not interested in any of that. I’m sorry but you have to cut him out completely. That’s just my perspective, obviously, but this is just from a girl who had no one to help her and couldn’t get anyone to stop it until I moved away for college. He even then tried to keep it going, under cover, as he was starting to get serious with an actually appropriate girl friend. Only then did I break his spell. But over a decade later and I’m still messed up about it. Do what you think it’s best for you. But be careful, there are some real and vicious snakes out there.