That's very sad suzie1. Five years ago, I saw a young man of the same age knocked over by a lorry.The driver of the large vehicle had no idea that he'd hit anyone, and when he was finally traced, the shock almost finished him.
The young person in question died shortly after being hit. He'd been listening to music through headphones and just wandered into the road without thinking. I shall never forget witnessing it all, and helped the police to pick up his things which'd fallen out of his college bag.
If you have some sort of religious faith, then you'll know that this person's now at peace. Others believe in visiting a medium or some such person, and swear that what they see or hear gives them comfort, but sadly, this person isn't going to come back.
If you perhaps volunteered to visit people in hospital, or took up some work in the medical field, it might help you. Seeing others in a bad way, or doing something constructive to help, could take your mind away from this particular young man, but yes, all these accidents are very tragic.