How do i stop this girl from taking my best friend?

I might soud like a loner but I REALLY DO NEED HELP. I have a Best friend and we've been really close, but this other girl is steeling herr away from me. On facebook they talk about me, even though the dnt say my name i still know 100% I really miss her too. But the girl who's stealing her is funnier and louder. I NEED HELP QUICK!