An alcoholic doesn't have to drink "all the time", or be a homeless bum living under a stairwell of an abandoned building. The issue is how does alcohol affect his life? You've already answered that.
One last thing, and this is just MHO - take the number of times and amounts that you know he has drank, and double it at a minimum. We alcoholics are experts at hiding it and you have already said he can consume large quantities with no apparent effects.