http://en.wikipedia.org/wiki/Schizoid_personality_disorder
Have a look and see how many of your 'symptoms' (although that word has very negative connotations) match up.
You know, it's funny, when I was seventeen/eighteen or so I was ridiculously social. I was part of the 'it' crowd at school (I'm not trying to boast here, I mean what fucking difference does it make now). There was a group of like twenty of us, about ten guys and ten girls, and we always used to do everything together, hang out, drink, chat, party. And we were genuinely close. I remember once, I think in my last year of A-levels (which would have made me about eighteen) one guy in the group, Dave, lost his mum. A few months later I was in the park alone with him and he started talking about her, then crying. For like ten minutes I was quite literally his shoulder to cry on, in front of dozens of people passing by. Yet I didn't feel in the least strange or awkward. He was part of the group and that's what we did for each other. That was who I was back then.
Then came university and my experience of depression. I hardly spoke to anyone during that time, which lasted maybe a year. When I was finally coming out of it, coming back to reality, I remember talking to my shrink and doctor and parents and asking: how do I get my friends back, when will they return? All three gave the same answer, which was that now I was 'back to normal' I would pick up friends naturally along the way again, just like before.
...But it never quite happened like that. I never got my friends back - the old ones or new ones - because I never quite wanted to have them in the same way as before. Someone asked me a year or so ago if I'd completely recovered from depression, and before I really thought about it I told them yes. But later I got to thinking, and I realised that I never did, not fully, not like I was before.
Maybe it was always inside me, maybe when I was young I was just faking it, but it didn't feel that way. Depression left me... cold. It made me a cold person. Am I lonelier now? Of course. But I'm also infinitely freer. I will never marry, never have close friends and never again be close to my family. But is that a fault? Am I broken, or just stronger? Will it help my life, or hinder it?
Check back in forty years, I'll let you know.