Honestly, I wouldn't try to wrap my brain around the reasons WHY an alcoholic drinks...there always seems to be a "good" reason, and yet, as someone who isn't addicted, I just don't get it. In any case, usually when we're looking for the WHY it's because we're looking to point the finger at something or someone. There's really no point in that.
The situation is what it is right now, so deal with today. Perhaps later on in counselling you can rehash the past, if it helps you, but there's not really any point to it at the moment.
I wish you luck and I hope that you come back and keep us posted on what happened.