Because it was fulfilling a desire perhaps?
I dunno about you but I could obsess about booze as much as I drunk it.
Like I said if you think you're depressed - go see a professional and checked out....at least you can either know you're dealing with something clinical, or you'll set your mind at ease that it's just the normal 'grey' period that a lot of us go through when the central focus of our life is taken away.
If it's the former there's lots of help for clinical depression.
If it's the latter - with a little time and effort you can make your life what you want it to be
Either way things will improve
D