The simplest assumption is just that something about the person changed, nothing more. It can feel like you're being abandoned or betrayed, and in a sense you are. Your old friend is leaving, and a new one is taking his or her place. When a friend changes you can find the bond that's connecting you at a deeper level. The surface stuff isn't a good thing to depend on.
Physical bodies change as they grow.
So do emotional bodies and intellectual ones. Take a deep breath. People move, life is more like a wild dance than a ceremony. You just can't tell what's coming next. Anger Anger is only dangerous if it's bottled up.