Awww, girl, I'm so sorry. <3 That's such a terrible thing to happen. I, too, lost someone I knew a few years ago. We weren't even that close yet, but it was still one of the most shocking, viewpoint-adjusting things to ever happen to me. I can only imagine what you are feeling right now. :'c
See, when people die in your life, it's like a reminder that we all go eventually. So for his sake, try to do the best you can with the time you have now, whatever that may be to you. And if you need someone to talk to, then you can always talk to me.
Your friend,
Twin~ <3