Best friends have to follow?

They don't but in this case he's apparently going to. Sorry if this isn't what you want him to do. But people move around all the time. It's certainly a curious point to be moving too California when so many of us who already live here are trying to leave. However, it's his life and he has to make his own mistakes. 

He is a BFF, they do that.

Someone who is insecure will do that. They cannot think or act upon their own ideas and wishes and must always follow what another person decides or suggests.  It's not a good way to be but it's a difficult thing to break that dependency on the other person.  Only when we begin making our own decisions 100% are we really mature.  Relying on someone else's ideas, wishes and instructions shows immaturity.