I lose my best friend too. I understand you. I know how bad it is.
Darling, don't waste your life because your friend is being stupid . She will realise that she was making a huge mistake.! If she doesn't, she's blind .
Stop partying, stop smoking and study harder. Trust your friends, trust yourself.
If you need someone to talk to, PM me and I'll be there for you.
I hope you get better xx