A good friend of mine once told me, A man is judged on how much he loves those closest to him.
You don't need to maintain a friendship just for the sake of it. Friendship is a dynamic concept - give a little, take a little.
Don't be fooled though, you do need to make sacrifices for your friends, perhaps even before they've done so for you.
Personally, I have many circles of friends. But only about 5 of my childhood friends I would say are close to my heart and know me well. They always seem to be there to fall back on no matter what, and they have lives of their own, they aren't needy, yet they all live more than 300 miles from me, i see them everytime I make my way back to my hometown...
It seems like the new friends I've made at college aren't nearly as close, maybe just 2 of them I could rely upon for support when I need it most.