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.
Be true to yourself, help others, make each day your masterpiece, make friendship a fine art, drink deeply from good books - especially the Bible, build a shelter against a rainy day, give thanks for your blessings and pray for guidance every day.