Frustrated hubby: my wife is also an alcoholic and we're twelve years married and 4 kids, and she's still in denial.
My advice: cut and run.
I know you don't want to feel like a jerk about this, but there isn't a good time or way to issue the papers so don't put too much effort into thinking about that.
Like the Nike ad says: just do it.
As for alcoholism being a disease: i think its more like a half and half. Both my parents died of diseases(cancer, and hep c) and I'm willing to bet that if staying alive meant all they had to do was just stop going to the bar and to stop buying their disease in the form of a six pack, mini, shot glass, whatever, they would have.