Are friends supposed to just drift away like that?

what do you do when you give and give to your friends and they don't return the love? i have a friend who i used to do everything with - we were attached at the hip - and then she started spending time with other friends. now shereally doesn't make any time for me. i have lost so many friends this way and it saddens me. is this normal? are friends supposed to just drift away like that?