I agree with you that change is inevitable and that to be able to adapt, we need to learn how to adjust to these changes.
One of the biggest shifts in my life would be when I lost the good friends I've had in college. Of course, I, too, am guilty of this because I was the one who started to be distant. But I learned that there are really friends who, even if you want them to, will not be there till the end. It makes me feel nostalgic whenever I reminisce the moments we've had. I kind of miss their company but I don't think we can still work our friendship out, as it has been years since we last talked.
However, I've also learned that in the course of life, we will meet more people who will make us realize why these changes occur, and will make us think that hey, things do change for a reason. Because when one door closes, another door opens.