I'm not sure about co-workers not being friends. The way I see it, once you enter full time employment work is the main place you meet people, the same way when you are a kid the main way you meet people is at school. Blocking out work as a source of potential friendships is blocking out more than half the opportunity. I don't think I've made any friends in the past 15(?) years that wasn't directly or indirectly through work.