Who knows exactly what is going on with OP’s son, but my gut reaction isn’t ADHD, depression, etc. He just sounds really immature, which is not uncommon with 18/19 year olds. My guess is that he is having a ball, enjoying independence, drinking, smoking, indulging in gaming obsession, growing up a bit slower than a tuition-paying parental unit would approve. Academic achievement isn’t really on his radar–kid in the candy-shop syndrome is winning out. Like many “high achieving” students these days, they are coming off an over-programmed rat-race high school get-into-good-college marathon, and jeez, who could blame them for enjoying the opportunity to blow off steam and enjoy the opportunity to structure (or non-structure) their own daily life in the company of other bright, interesting kids?
Sure most kids at top colleges also have an academic or professional drive that overrides pure id, but I think there are quite a few who are enjoying the social experience more and only barely tolerate the academics that “interfere” with their free time. Anecdotally, seems more common in kids coming from highly controlling parents. (Bro flunked out of Dartmouth, sister narrowly avoided same at Hamilton. And thanks to a bunch of APs I made it through NU, but recently took a look at my transcript, and wow, a lot of W’s from classes where I just couldn’t bring myself to write those pesky papers. Sis is full professor, I’m a master teacher, bro retired public servant, all doing fine in long run).
With the full-pay price of college now, I can see OP’s frustration with “wasted” tuition and sympathize with desire for son to do the growing up first, then spending tuition $$ where it will count, but I don’t think I would pathologize son for being immature and undisciplined.