Situation of deep depression

I m in grade 12 high school. I had a breakup 2 months ago and it was kinda my mistake that i was just angry and said to the girl that we r done... But after that I begged for forgiveness from that girl for 3 weeks but she didn't forgive me. Even my 2 best friends ( a guy and a girl) also left me and went with her. I am totally destroyed emotionally. That guy best friend, well he and my ex girlfriend are best friends, sharing same locker and just together all the time in school. That kills me even more. I see them everyday in school, together, having fun and enjoying and I am just there. I begged from all but they don't care. I need some advice as to how to divert my mind and not be depressed seeing them daily.