I'm 18 now, but when I was 16 and 17 I found myself wishing my teenage years away. Like you, I hated school - I'd had bad experiences making friends (and in my final year I didn't have anyone at school I considered a friend at all, just some acquaintances), and I didn't feel I fit in. I didn't go out at night, I'd only ever had one "relationship" (if you could call it that), and I spent most of my time at school by myself.
Turns out, though, that when you turn 18, you may legally become an adult, but you don't stop being a teenager! There's still time to experience things you feel you missed out on at school. Since I started university, I may not have found a boyfriend (still early days yet, though

), but I have started going out some evenings, and although it can be hard, there have been times when I've actually felt like I fit in, which very rarely happened during school.
Anyway, what I'm trying to say is that even though you don't feel like you can be a teenager during school, school isn't your only time to be a teenager. 18 and 19 are teenage years as well! And the people you meet at those ages will generally not be the ones you already know, so they won't judge you - you'll have a clean slate.
Not sure I've been much help, but I hope you feel better soon.