If he got drunk every night with friends or a few times a month, his attitude to alcohol was a frequent subject of your dispute. Maybe he is not in the stage of hiding bottles of vodka in my dresser, but you had reasonable suspicion that he drank a lot more than most people, and especially you, seem. Forget that the alcoholic will be able to alter or that he will change for you.
He played in the slot machines or even experienced drug addiction? Now he wants to go and claims that their addiction without you will never be able to overcome, and you are his last hope for a ticket back to a normal life. He emotionally blackmails you and makes responsible for his fate. Don't let him manipulate you with his addiction he needs to fight in the first place, myself along with expert advice. You can offer support, but do not try to cope with his problems alone. More likely is the possibility that you will roll down the incline together.
Did he ever slap you? Then the choice is clear. In no event and under no circumstances do not give him a second chance. The violence there is no excuse, no one has a right to it even in anger. The man who hit you once will do it again at any time.