Moment of truth!
What actually remain are such moments, people change but moments are framed as memories and bring smile or give a taste of how we experienced such moments.
We meet new people and create new moments, so lets it is vain cribbing about those who changed.
It is not that they have changed, it is just that they don't fit in these moments any more.
This is one fraction of my understanding on change, let the change be among people or environment or things. But moments remain same as we remember them.