This may sound awful and I really do feel for the family of the dead boy but his death my be the best hing to happen to your nephew.. if he is experimenting or contemplating it he has just had the biggest reality check imagineable... Most boys don't realise they are not immortal until they are in their mid 20's... your nephew has learnt the hard way at 15 that life is very delicate and it isn't just 'old' people who die. Chances are his friend's death will be the wake up call he may or may not have needed to really value what and who he has and how precious his life is.

Make sure you let him know you are there if ever he needs an ear as the grieving process at his age is pretty traumatic (especially for boys). He is at the age where he is trapped between boyhood and manhood... he is likely to feel that he needs to be tuff and not show how hurt or upset he is, to not be 'week' when really he may just want a good hard cry and to be told everything is going to be all right.

I lost a friend to a heroin o/d when I was 14. It was hard for the girls to deal with but it was the boys who suffered the most.