daddywillbehomesoon - You have had lots of fantastic practical and emotional support today, and I know that you are drawing strength from it. I just wanted to send you a quick message as well and to share something of my experience.
I ended my marriage over 2 years ago after many years of emotional abuse, infidelity and alcoholism (his not mine). It took me a full year to tell him to leave though from when I first woke up to what was going on, and started to speak to friends about stuff that I had worked really hard at keeping secret.
In some ways I regret having wasted a year of my life - my friends knew that trying to save the marriage was a lost cause, and I think deep down I did as well. But like you I was consumed with anxiety and guilt about the children. Taking my time, trying everything I could to make things work meant that when I did make the decision, it was the easiest, and quickest one I have ever made, and I didn't look back for a second - If I had ended things when everything first came to light I would have always wondered if there was anything else I could have done.
I am not suggesting that you should stay in this horrible situation for another year - and I should also stress that I never felt physically threatened, but if you come to a point, as I did, when you know that you actually have no choice, that all possibilities have been tried, then the decision, and your plans for the future will be so much clearer.
To be tackling your drinking at this time is a brilliant first move. I didn't even acknowledge that my drinking was out of control and I felt like I was wading through mud for months, everything felt like such an effort. Being sober (mostly) will help you see things much more clearly, help you to attribute the crap behaviour clearly where it belongs, knowing that you have not contributed to it in any way, and hopefuly give you the confidence that you need to take back some control in your life.
I am thinking of you and feel sure that when you need to you will make the right decision for yourself and your children.