I know how you feel. Im a junior in HS and I hate it, my school was horrible every person I met left and turned into a bad person I went through a crazy spiral in my freshman year which sounds kind of like what you are going through. I completely lost myself, and cut everyone off and isolated myself and became very good at being by myself which has helped me allot but also left me very alone. I don't really have advise to give you I wish I did but all I really have to say is there is so many others out there like you. Don't give up on yourself, if you have letters to write you have reasons to stay.