i've gone through periods of years without seeing certain people. in some cases we carry on as we left off, in other cases it's akward and not the same.
it's pretty normal to grow apart then come back together later on so don't worry. in the mean time concentrate on bettering yourself and persuing your own personal goals. that way when you catch up with people later on you can share your progress and you won't feel left behind.
try and have a bit of trust in the process

i think true friends are there for life, and they stand the test of time and periods without seeing each other. i'm going through those periods now in fact with a couple of friends. one in particular right, i don't like the circle of people he knocks around with, i don't get on too well with his g/f or his situation. i haven't seen him for 2-3 years and it may be another 2,3, 5, 10 years til we hang out again, i don't know. but it'll happen one day.
BTW there's a line from [i think] the Bhagavad Gita [spelling?] - lift the self by the self, never let the self droop down, 'cause i am my only friend, i am my only enemy.