No point feeling upset, it was a kind gesture made in good faith and if you hadn't given him that bottle he would just have bought one anyway.
Worry for him not yourself.
I'm sure that wasn't the only source of booze he had, if he's not drinking the one you gave him he'd have something else. Don't worry about it, still a nice thought
I just feel a bit stupid not figuring out that he might have a problem. I've seen it in my own family, can't believe I didn't realise it was going on in theirs.
I'll be a bit more careful about buying booze as a present in future.
I know I've not turned him into an alcoholic by giving him a bottle of whisky, it's just that I really would have been hard pushed to give him a more inappropriate gift!
I'll move on from it though, not worry about it too much. I know my one bottle probably wasn't the only one he was given or the last one he will drink.