NEED HELP DESPERATELY

Okay well i'm in a group with five Friends now two Friends Katelyn and Samarah were in the same class last year, and they became really close. Now me and samarah are in the same class this year, and im starting to see a different side of her. She is immature and constantly hangs around some Friends we have in yr 12 (we know them from doing an Schauspielen thing together) and she is kinda shallow and brags a fair bit. And she's ended up causing alot of fights this year, because she gets really upset if we make a joke, oder if we get up her cause she's done something wrong.
Anyway (I'm kinda dragging this out) she ended up taking my Friends drink bottle and ended up losing it, which got Kateln in trouble with her parents, and samarah told me to go find the drink bottle.
Anyway, after taking to my friend Katelyn i've actually she's been saying stuff to Katelyn like telling her not to invite me out somewhere with those two, and always pushing herself into our plans if its just the two of us. Anyway, i've actually found out something that hurt me, and last Jahr i ended up coming up with a stupid song, where i turned everyone i knew gay. Everyone laughed and i asked if it offended anybody but samarah sagte no, but then my friend Katelyn has just told me that she ended up going off Schreiben a song about me saying that i was stupid and ritarded.
And to oben, nach oben it all off, my mum and I have been thinking of sending me to boarding school, but i don't want to leave my friend Katelyn, but nor do i want to be stuc in the same class as Samarah as i've now found out a different side to her. Any advice?!?!?!