U sound very stressed. First of all, no..this isnt ur last chance but try to break the pattern. Its true that it becomes easy to bear school if u have friends there too, but if u dont have friends then skipping school still wont do any good. I remember when i was in high school i spent a whole year without ANY friends in class..n i dreaded the free periods and break time. My friend had changed school and as i used to be with her all the time i didnt have any other friends when she left. But eventually people noticed my presence again and i made a couple of friends thereafter.
As far as studies are concerned, m a lot older than u are BUT i still find it hard to concentrate and study well. But im not quitting just hang in there and dont lose hope. I'd suggest may be talking to an elder (if seeing a therapist is not an option for u) about how u feel about ur career and life might help. Just dont quit school. Try to be nice to people, be courteous and people Will notice u and would like to become friends.