I could think of several people to put here.
In high school, there was a group of us, Laura, Melissa, Keri, Marie and me! We were together alot to say the least. Laura was a year older than us. After Laura graduated...things just seemed to fall apart. I don't feel that Laura was the glue that held us together...I think we all just started changing. Through all the years (graduated in 97) I really only kept in touch with Melissa. Laura, Keri and Marie are my facebook friends...but really, we never comment on one another. Melissa and I have a good email talking about life every few months (speaking of which, we are overdue).
I think in reality, after high school it is hard to stay close to the same people. You find your self and everyone grows in a different way. I guess that is ok, I have had friends to take their place, but I still miss them from time to time.