Oooh pick me! Pick me!!! I've got answers!!!
Not really -- but I've fought the evil ghost of guilt. Guilt is a useless emotion. You are leaving him because you want to regain control of your life. You are leaving him because you want to protect your children.
You don't want to rob the children of their father? Well, someone here pointed out to me that it's significantly better to have no parent than to have an alcoholic for a parent. And here's my thing: If your children's father wants to be a father, it's up to him to make the effort. No amount of you staying in town or staying married or "helping" him be a father is going to do the trick. HE is the only one who can make the choice and the effort.
Here's another thing: Think of it this way: If the only way you could be with your children would be to -- oh, say, drive an hour every weekend, or fly across five states once a month, or mortgage your aunt and sell your cousins to aquire enough camels to ride across the desert to see them -- wouldn't you??? That was a HUGE eye-opener to me, when I realized that the slightest inconvenience made it pretty unappealing for my AXH to see the kids. It was too hard, and he was not willing (once again) to make the effort (just as all those years we were married).
I think what we suffer from is some kind of survivors' guilt -- you know, like survivors of plane crashes where others died? The truth is that HE chose the situation he's in. You can, through Al-Anon, get the support you and the kids need. They have a great brochure about how to talk to kids about alcoholism, and I love how it manages to be very straightforward without being judgmental about the alcoholic. (I used it with my youngest just an hour ago...)
Keep on keeping on, and don't fall for the quacking. Hugs.