i'm in the same boat as you. my ex and I just split up. she was my best friend. i saw her almost day. we talked to each other about everything.
if you would've asked me a week ago, i would've told you i want to fix it, and get back together with her. i didn't want to hang out with anyone. i just sat at home depressing the shit out of myself.
then a couple days ago, i decided it's just not worth it. i've gone out almost every night. i'm hanging out with new girls without being stupid and jumping into anything i'd regret. you just have to get out and have fun. tell yourself that she's not worth this. go out and find someone appreciates you. and it doesn't have to be a girl. just spend time with people who care about you and it will all go away.
am i completely happy right now? no. but do i feel ten thousand times better than i did last week? absolutely. every night i go out and do something fun.
so basically, get off your ***, stop feeling sorry for yourself, and start living life.