I've been thinking a lot about this recently and I think, even though I have some cool work colleagues who care about me, I just don't fit in with them!
I guess I knew it anyway but this lifelong feeling is still very much alive, just as much nowadays as it was wheb I was at school. I feel that I am only friends with them because I have to be. I wouldn't choose to be friends with them.
It's a similar thing with old school friends. Fair enough I don't keep in contact with any of them apart from seeing the odd update on the Friends Reunited website. But I would never choose to be friends with them. I wouldn't want to get back in touch with them either.