How should I deal with a friend whose making a very bad decision?

Give him a chance and try to understand her since he's your friend. You can make him take the right path. Do not talk to him about this again but it's really your choice. I suggest let him decide this one and realize it all by his own.. Stay friends with him and if his decisions annoy. Try not to make it your business and find other hobbies. You can't do anything.. Though you tried. That's all that matters.