It does sound like he is depressed. He sets standards for himself that become burdensome, like taking those heavy duty classes. He needs to lighten up, unless he has some great passion for academics. He sounds like a basically good kid. It does sound like you are on the right track. How nice that he was so industrious over the summer. Maybe he could find a study partner in one of the science classes, as an alternative to the pot smoking buddies. Maybe you could offer to host a study-a-thon for the next big test. They study together and you make special eats and treats for them. There is much there to be hopeful about. He will make mistakes and know some heartbreaks. That may be part of his destiny. He mainly needs to do well enough in school to have good options vocation-wise after he graduates. College is not necessary for every kid. I have cousins who went into trades and are doing great, better than some their age who went to college, just to languish without work afterwards.

Then, again, if he picks things like Physics to study, he may aspire to more than a trade. That's okay too. Best of luck.