There's not much a person can say but it sucks. I agree with remembering the good times.
When I was 17 my buddy & I were duck hunting & he drowned. I was the last one with him. My mom told his mom and I told his dad. I'm now 56 & still have days that it bothers me.
Here's what I can say to you. Don't let it get you down. Don't get caught up in "drinking one for him". If you feel yourself getting depressed, get out of the house and do something. The cold facts are that people die for no good reason. Accept it.