Its tough, but its part of life.
Cant expect friends to be always there for you. True they are great buddies who, Im sure, will aid you in your hour of crisis, but they got lives too. Some got family, some got relatives, some got lifepartners.
You will always hold a special place in their hearts, but their world, their life , their bigger picture is not your monopoly.
Never was, never will be
Get on with it. Thats life !