OMG OMG OMG ! I NEED HELP !?

So I have a big problem. Its with my bestfriends. Well one of them Isabella. She used to like this guy named Adam (Back in November) & She hardly knew Adam she saw him after one day & then all of the sudden started liking him when she has never even talked to him before. I met him in the beginning of the year which would be, I knew him for about four months. We had 6th period together & sat next to eachother. I always had feelings for him. & then one day he asked me out , & after about a week of complication I finally made my decision & would go out with him I asked Isabella if it was okay with her & she said she didn’t care and she was alright with it. So then I went on & went out with him. The time while we went out she was not acting like herself & was acting different. She wasn’t smiling she was spreading apart fomr me. I couldn’t take it anymore so I had to break up with adam after two weeks. It was alright though. Now I don’t have any feeling for him anymore. So now I have another bestfriend Juliette & Isabella is her bestfriend too we are all like the three musketeers. Isabella liked this Bryan kid, on & off. Isabella was confusing about it. She said she didn’t like him one day & then the nesxt she said she did. & she called him ugly & fat one day & cute & hot the next. She couldn’t never seem to make up her mind. All three of us were friends with Bryan & we talked & stuff. Juliette talked to bryan a lot too, Then one day Bryan asked out JULIETTE not Isabella . Isabella got pissed, but Juliette said no cause Juliette knew it would strain their friendship. So now her & Bryan are just FRIENDS. & Now this new kid named Dominic came along. Isabella really liked Dominic & then one thing turned her off about Dominic & now she is all over the place. . She said she didn’t like him one day & then the next she said she did. & I was at her house & So was Juliette He asked for my number. & Now Isabella is crying & all depressed cause she thinks the same thing will happened to her with what happened to bryan & Adam. I don’t know what to do. She said she wants to kill herself & she is going to cut. If you look at my previous posts you can see that I once have cut before. But will never do it again cause I know it does leave scars & doen not accomplish anything. So I yelled at Isabella saying that if she cuts herself & I see marks on her arms Monday at school tht I WILL tell a parent. She said she doesn’t care and she just wants to die. I don’t know what to do. She is all MAD AT ME. Cause she cause I don’t know whats he is going through . Since this has happened where she likes a guy & the guy she likes just goes for juliette and i. Its not my fault, I’ve been trying to help her but I don’t know what to say anymore. Cause all she said is that she is ugly & fat. Which isn’t true, she gets flirted with the most guys out of me & Juliette. What do I do, what do I say. Im lost & confused.