My best friend is a whore and it's starting to affect my relationships with other friends?

Okay, so, it's her own business if she has sex or not. I mean, we're 14 and she's done things with at least 5 or 6 guys, and I think that's a bit much...But that's not my business. My problem is that she decides to do things like this either with my friends, or friends of my friends.

She'll have a boyfriend, then get naked on webcam for all these other guys, while she has a boyfriend. Then, he'll find out, and get mad at her and break up with her. Sometimes she also cheats on people who she's with, but then she seriously freaks out when they LOOK at another girl.

I was her girlfriend at a point, and when she started cheating on me with my best friend, she claimed that she had decided she preferred being with guys because of sexual reasons. But then, he broke up with her, and she tried to make me pick sides. They had went out for a month, and she acted like they had been going out for years. She would just complain and complain to me about him, then continue to force him to talk to her. (Threatening to kill herself, etc.) While they were together, their whole relationship was based on s*x. They'd do it every single day, and she'd get mad if he was busy.

She stopped being friends with my one friend because he got a girlfriend, and she liked him, so she decided that now she'd hate him. So, if I even mention his name, she goes off on me.

She was sexting my other friend's boyfriend and got really angry at me when I took the other friend's side (since she basically forced me into taking sides again). She refused to hang out with me a couple of times because the friend who's boyfriend she did this to was there with me.

Her and my other friend had oral s*x in a dressing room at the mall the first time they met. They were never in a relationship, and my friend made that quite clear to him, but she freaked out when he spoke to one of her female friends because she thought he was cheating, even though she had cheated on him many times. Now, even though he did nothing, she hates him and won't talk to him.

She tried to get a 20 year old to have s*x with her at a party, and she was flirting with my 18 year old friend who has a girlfriend and keeps sending him sexual pictures even though he told her to stop.

Two days ago, I was at a friend's house with her, and I was sitting between her and this other guy. She kept making suggestive comments to him and letting her chest show (like, her shirt "falling down" "by accident".) And eventually, knowing this guy had a girlfriend, she leaned over me and started making out with him. He said to her "I have a girlfriend", and she tried to get him to cheat. He ended up doing just that, so it was partly his fault, but she shouldn't have tried. The girlfriend is one of her friends. He told her "we're not going out, this was just a one time thing", and she flipped out. Right in front of me and three of our other friends (before he told her they weren't going out), she started rubbing his thighs and his crotch, before giving him oral s*x after me and one of the three friends left (I know this because she admitted it after the other two friends told me). Now she's trying to get me mad at him for not wanting to be with her.

Through all of this happening, she had a girlfriend who thought she was not cheating.

Now, if all of this were to happen and I were not involved, it would be none of my business. But she's hurting my friends, and making me choose sides. And when I don't choose her side, she sighs, rolls her eyes, mumbles "whatever", then refuses to say a word to me for a long time....until she needs something or has something else to complain about.

She's been my best friend since I was 10, but I'm really getting sick of her.