Best friend passing away

Needing help at the moment... so 8 weeks ago my best friend, a boy I had been dating on and off for over a year passed away in a car accident. He was 17. The 17 year old girl who was driving, went through an intersection where she was meant to give way and he was the passenger and got tboned to his door. Minutes after the accident I was the first one on the scene sober driving home from a party... had to watch it all happen.. he was in a coma for a week until we found out his brain injury was so bad they couldn't do anything more... I can't even close my eyes now without seeing the accident or him... I'm having bad thoughts to.. just don't know what to do at the moment...