My friend is very, very sweet, but about a month ago, she decided to leave our lunch table and now rarely talks to us. She does ballet, and there is this girl who she does it with. They see each other a lot, so it was natural for them to become friends. Gradually my friend started sitting with her more and more, and making up bad excuses to do so, like, "Oh, we have some ballet homework to do." I was angry at first, but then reached out to her and asked her what was happening. She said it was nothing I did, but what some other girls did. I feel like, if it's nothing that I did, why is she ignoring ME? The girl that she started sitting with used to be nice, but now she is mean, and a bad influence. My friend used to be totally innocent, but once she started hanging out with this girl, she says some inappropriate things. She was my best friend! My other best friend has come to terms with the idea that she won't be our friend anymore, but I can't. I miss her. What should I do?