time is a fickle puppetmaster
Well, okay--I'm not that deterministic. Time isn't a puppetmaster, but it's strange and sometimes sad how people cut ties with each other. Those with whom you had thought you could be friends with for life suddenly disappear and move on--or even worse, disavow connection with you for reasons unknown. Others decide that they're too good for you and do the same. True friendship is never a zero-sum game, and it should never be that way, lest friendship turn into a manipulative relationship between two parties seeking to exploit each other. Tozer says it best: "Very few things in life matter." The relationships people build between one another are certainly some of those things.