Losing a friend like that is like breaking up with a boyfriend/girlfriend, but no one really talks about it. I lost what I thought was a very close friendship when I left a job and it still bums me out, three years later. You aren't alone in confronting a situation like this and wondering what you could have done differently.

Not sure if this will help you, but in googling about this friendship problem, I came across the concept of 'proximity friends,' people we are close to because we are close to them. When we lose the physical closeness, the relationships sometimes fizzle. Perhaps for you and I, what we thought were real friendships were proximity friendships to the other person?

I hope it gets easier for you as time goes by.