I know this too well... My childhood friend who was my neighbor ever since we were 1 year old and was/is like a sister to me moved to Stockholm many many years ago and sure we still keep in contact by sending SMS to each other on Christmas/ New Year or when either one of us has a Birthday and we try to meet when she comes home to visit her parents but that's it, I don't have contact with anyone else I went to school with or were friends with before.
But that's just life, people grow apart and move on with their life.
Yep! It happens!! We all die alone ;)