I've been thinking about this situation since I read your post. I keep coming back to the same concern. I am wondering if your efforts to shield the girls from the of your situation is in fact causing them more harm, or delaying the grief that they may feel over the situation.
I know for my own kids that the years I tried to keep him in the home for their benefit did more harm than good. I'm not going to lie, the past year and a half (when we were both finally honest about was going on) was completely horrible for both of them. They have suffered emotionally, physically, and scholastically. But, I can tell you that they are emerging from the wreckage of that discovery as stronger, more independent, and realistic kids.
I think you keep reaching out to him and trying to get him to be a dad, but he just isn't there. He isn't capable of stepping up right now. He may never be. I did the same thing. I told myself over and over again that a bad dad was better than no dad. They have both told me they are glad he is gone and they do not ever want him back. I also think I may have subconsciously used the kids as an excuse to pursue him or persuade him to stick around. I hope that isn't the case.
