its prob depression....everyone is different but attemped suicide is generally a call for help. if i was going to kill myself i would, or at least put myself in hospital for ages. from my experiences, first thing i would do is look into this alco problem. at least slow it down.
next thing to do is to get him to see a future for himself, one where it is possible for him to be happy in...no harm in trying, right?
life is short enough as it is...may aswell enjoy it.
i wouldnt sugest informing parents or getting onto docs straight away, to me that would just make him feel less of himself(which could be the prob)...but i dont know the sorce of his problem, so im only guessing
if anything...just be yourself...be a mate and im sure he'll know he will only be losing out if he goes.