I think there are a lot of different ways to view friendship. One construct that I've found reasonably helpful is this idea of friends for a reason, friends for a season, friends for life. You shouldn't hold the bar that everybody has to be a friend for life or it's not worth having. It's easier to make friends than we think if we're just a little more proactive about it.
How do friendships change as we get older? Should you join a bowling league? And is Angela more important to Mike than Mike is to Angela?