A lot of people change for good. Some people just fall off. Just trying to progress in anything, no matter what you're doing, I feel like any progression you make... some people aren't gonna be around you that were around you.
We are in a survival mentality, and that's hard-wired into our humanity, because we are the winners of an evolutionary struggle of millions and millions and millions of years.
Believe in yourself! Have faith in your abilities. Without a humble but reasonable confidence in your own powers you cannot be successful or happy. But with self-confidence you can succeed. A sense of inferiority and inadequacy interferes with the attainment of your hopes, but self-confidence leads to self-realization and successful achievement.