I moved away from home 11 years ago, and my friends' effort at maintaining our friendship has been quite surprising. Some of those that I was inseparable with in high school, I rarely hear from them. They are busy. Some of those that I was just casual friends with, I now interact with on a daily basis, and I have come to know them much better than I ever could have hoped to. Some of those who I barely knew have become my closest.
What I realized is that when I was putting so much effort into trying to maintain the friendships of those who didn't reciprocate, I was really causing myself stress, and it was preventing me from building a life HERE with new friendships. Over the past few years I have stopped initiating contact, and just make sure to send Christmas cards to those who seem too busy. Instead, I have focused on making new friends here. It took me 10 years, but I FINALLY have a few close girlfriends here that I can rely on, and who can rely on me.