I think perhaps you're suffering with a lot of self doubt. Maybe a low self esteem/confidence?

Anyone can go to school. You're obviously not stupid (I can tell just from reading your posts), but I know that doesn't mean you don't FEEL it. But honestly, even if you weren't the brightest spark, you could still do relatively ok in school. I went to uni (quit, but still) and I knew people who weren't exactly academic, but if you put in the effort you can do well... the work is not THAT difficult! (ok well in the UK standards are way lower lol, but still, nothing you're given to do is impossible). I'm sure you're much much more clever than you realise, though, and you will do fine. And the point is that you don't know this stuff, you're there to LEARN it, everyone is equal in that. Once you settle in you'll realise you can do it

Maybe you haven't found people who fit you. You don't have to fit in with others, let them fit in with you :P ... when you find a bunch of people who are similar in some ways, you'll probably feel much more comfortable (example, my brother is a bit 'weird', always been a bit of an outcast socially... and then he met a load of people who were also 'weird', and hey presto he fits!! And that was at the age of about 27. I hung out with them and... I didn't fit in, lol).

You'll probably meet people in college who you get along with. It just sort of.. happens.
Perhaps join a group, or going back to your hockey team?

Do you think you'd benefit from therapy or medication? Sometimes those things help. I'm currently reading a book on self esteem, only a few pages in but... I do think EVERYTHING is easier if you have an at least ok self esteem.

Good luck x