Oh, uni can be very depressing, made all the worse by having others whooping it up, living the dream. It's a bit like going to a party and not enjoying it, while others are - you feel worse than if you'd stayed at home.
There is not a wide mix of people to be with, they are all young. Some love this and ride the crest of the wave, but it felt very truncated to me, very narrow, not helped by the public school mix and having lots of young people a bit messed up by a very intense academic upbringing (not saying I wasn't it, but uni offers no escape from it). I tended to enjoy doing temping work in the summer hols more than uni itself. I just felt like I saw through everyone and everything at uni.
Then you have stuff like, when the summer arrives and the sun comes out, it's not uni any more. It is only in unseasonable months.
Also, it's harder on blokes imo when they hit this age as all progress stops. Until now you have a full programme at school laid on, you get older, shoe size goes up, pubic hair, you can legally smoke, drink, vote have sex and so on. Come the age of 20, everything grind to a halt unless you have put into place specific plans to ensure progress and excitement in life.
No one likes to admit to hating uni cos it's so enclosed. I never really met anyone who wasn't a student when I was there, and since I left I never met any students either. So saying you hate student life is a bit like saying you hate life itself, as one is wrapped up with the other.
Your son has my every sympathy, as it is very hard to quit and throw away a 'winning hand'. He has been told one thing and is experiencing another.