That happened to me too. But you just have to keep your chin up and move on. And maybe you could make more friends. I know I did. Lots of people will come & go out of your life. But you can't let that bring you down because there's always tomorrow :).
2 of my best friends left, as well. It was hard, for awhile. I have other friends, but they weren't as fun, or it just wasn't the same. The best thing to do, for me, was to keep in contact w/ them, and plan visits on both sides. Also, find someone who likes to have fun in the same way as you. That makes the time much easier.