What are friends?

As a being who lives life alone all the time, this question just pops up in my head, yet I can never answer it. I used to have a best friend, but I think I'm slowly losing him to a relationship. The sad thing is there is nothing I can do. My other friend will be graduating soon and going to Ohio and now I will be all alone through the rest of high school. Maybe it's best that I don't make friends, but live in a dark world of my own.