YOU didn't make the choice to end his parenting - - HE did.
What helped with my kids was continuing to explain and reinforce that "daddy's " behavior had NOTHING to do with them, that they were and always would be worthy of having a truly good parent, and that "Daddy" had a problem with alcohol that made him forget how to be a good parent.
Kids that age think the world revolves around them, and the downside to that is that when they are treated badly, they think they must be to blame, and only if they had not done this, or done that, daddy would have treated them better.
So keep reassuring them that they are worthy and wonderful, and that it is a real shame that Daddy just can't understand how a good dad behaves.
ShootingStar1