YOU are not the reason he drinks. YOU cannot make him drink or not drink. Or want to drink. YOU are not that powerful. When he tells you that you are the reason he wants to drink, what he is saying is that you are the EXCUSE he wants to use to drink. Big difference. Keep that in mind always. I have to remind myself of this sometimes multiple times a day.
Also, good job on not engaging. It sounds like he was looking to pick a fight to be justified in taking a drink and you didn't give him the ammo he needed. Well done.