Confronting him, only gives him more excuses for his bad behavior. He will blame others and not take responsibility for himself. He is displaying addict behavior! You cannot make him responsible. He has to learn that for himself. He will realize one day what he has lost. Do you really want your son around him right now? If he is using? And even if he isn't, he is still displaying addict behavior. FOCUS on you and your son. Take all that energy you are wasting on drug addict father and put it on you and your son. You and he deserve that.
I know your pain, it is soooo hard.