My therapist told me, "When one person changes, the relationship changes." No truer words have been spoken, as far as I'm concerned.
Unfortunately, the change to the relationship isn't always for the better. I've experienced this as well. I've found that some of my relationships had to go south because they were in reality toxic...to me. Others have become stronger, because those people are being authentic and are on paths of growth as well. Others have just faded away, because while they were not toxic, they don't relate to me anymore.
I've noticed that a lot of people just plain don't like change. It scares them. especially if its a change that reveals their shortcomings...words not matching actions, being passive aggressive, being the continual victim, etc. And in those cases, I've decided to let it fade away.
There is a saying, can't remember it verbatim, but the gist is, some people come into our lives for just a season (or period of time); some people come into our lives for a reason (and once that reason has been fulfilled they are no longer in our lives); and some people come into our lives for forever. These are the true friends...and they ARE few in number...but they will love you in all of your stages of life, and vice versa.