I think you did fine. This parenting thing is a lot harder than it looks. There isn't any good response to your daughter's question, there's nothing that can make his behavior okay.
In similar situation I told my daughter that there are two kinds of love: the one you feel and the one you do. Her dad can feel love okay, but he has problems with the doing part of love. This was in regards to a situation in which her dad has failed to act in her best interests, and she knows it. And I'm sure he knows it too and reaches for the nearest bottle when it bothers him.
I don't vilify her dad, but I don't sugarcoat him either. His weaknesses are something she has to come to terms with eventually and I can't protect her.
hugs
BG