Loner here.
Very occasionally I think it might be nice to have a friend to accompany me to places I want to visit, but for the most part, I'd rather be without friends. I find them very intrusive, very emotionally demanding. Once someone has decided that they're your friend, you can't get rid of them - they can't seem to comprehend the idea of wanting time to yourself and act all hurt when you don't want to see them and talk to them every five minutes.
I also don't like constantly having to censor my thoughts/interests/dress/behavior in order to make sure that my (so-called?) friends don't reject me. I don't want to have to hesitate before I do something, worrying what all my friends will think of me; to have to moderate my life to make myself acceptable to other people.