No. You are not responsible for his drinking, his not drinking, keeping him from drinking, monitoring his drinking or any of that. He drinks because he wants to. He drinks because he's bored, scared, happy, hungry, thirsty or the name of the day ends in y. Whatever it is its neither your fault or your problem.
Are you going to al-anon? I have found that it has helped me greatly and brought me back from a very dark place to a place where I am happy, centered and content. I highly recommend it.
Your friend,