Is there a counselor at school you could talk to? Someone just for You.
Also, it is okay to let someone know that you are struggling----you don't have to be stuck in the middle, it is okay to say "I'm not getting in the middle of this argument, I care about you but I can't do this" It is okay to say "I need some time for myself", and even to find small ways in which others could help you---you help your friend with school work. Is there something she can help you with? Also, know this is not forever.
Another approach might be to get involved in some activities outside of school (a local meet up, hobby...) with people who aren't looking to you for anything.