Listen, all these people on this board are too politically correct to understand any kind of nuance or circumstance. He's a horny little kid. You say in private he always respects when you say no. I would say, talk with him sternly in private again. Tell him that when you say stop, you mean it, and that if he does it ever again, if he ever forgets, it's over. Look him in the eye and dont be afraid to add a little anger/force into your voice. Tell him that you like him, but that if he doesn't respect your wishes, it's over. Then see how it goes.

I think this is a case of just a horny little kid who lets his hormones just get completely out of control. Like you said, you get confused between "yes keep going" and "no stop". Its teh same with him. While you're worreid about getting caught in class or whatever, his hormones are simply bypassing that "shit maybe we shouldn't" red flag that is successfully happening in your head.

I say this because I was a horny kid once too, and I probably did stuff like this in class with girls I was messing around with. It wasn't me ignoring their boundaries, youre just a dumb horny kid who just keeps wanting to put your hands down there and explore this wonderful sexual world that you're brand new to. Those hormones are powerful and its the reason teenage boys jerk off 3x a day once they figure out how to do it.

Its not your fault you froze either, dont put the blame game on yourself. Just have that stern conversation and if hes not doing what you ask, then drop him. But I would have that conversation first, if you really do like him. He might not have such bad intentions as other people in this thread are assuming.