People say that our friends circle is getting shorter with our age

How much this is true because I felt that most of my old friends are getting detached with time and I am also involved to do that as I felt that I should remained detached from some of them as they didn't change their attitude from childhood. They became friends as my popularity in school and college were increasing, but as my time changed they came back to their true colours.
I felt sad as one of my nicest friend got detached from me. In fact she was the only girl I loved. But she wasn't interested so we kept that upto friendship. She is in touch for almost 16+ years. But I understood her detachment because time should change. Maybe she decided to remain detached.