You can't protect your daughters from emotional disappointment--alcoholics let people down on a constant basis. Al-Anon or Alateen would be good for them, most likely.
It really doesn't matter "why" he is behaving the way he is. You're already planning to divorce him. You can make yourself nuts analyzing his motives, or you can appreciate the fact that he's making life a little less difficult right now, knowing that it most likely won't last.
Hugs, you're doing great.