I think it's not only this, but that the process repeats over and over. I had very deep relationships in high school, forged new ones in college, then both of those ended. I moved to a new city where I started a new job with a bunch of other people in their mid-20's, and we formed yet another community. Then the company laid off or required everyone to move to a new city. New job, same story again. I still start up new friendships at work, but it feels less and less worth it each time and so I try a little less hard year by year, because you're working against impersonal forces that will upend your social structures on a whim, and it feels like a treadmill to try to keep them intact.