Growing Apart

There comes a time, I think, in every person's life that you see the people you love slipping away from you. As we grow older you and your friends grow apart. People that used to be your best friends suddenly never want you over, don't really tell you anything about their life, don't listen to the things you have to say, and suddenly they seem to be mad at you more often. You see that you're friends are focusing on leaving and will do anything to do so... even if that means leaving you behind. I've experienced this and it breaks my heart. So what do you do when you've realized that your best friend has dumped you? Any thoughts? I for once don't really know or even have an answer...