What the Hell is Going On??

My STBX has always been a piece of garbage.  Yes, he takes care of the kids during the week when I am at work and he is off.  he picks them up from school, feeds them dinner and brings them home.  But in reality he is a babysitter/taxi.  He is not a father to them, he ignores them as much as he can, letting his mother take care of them, because they stop him from talking to his whore non-stop and spending every free minute on the computer.  He will go days not speaking to them or seeing them, doesnt even give them a second thought.  In his mind, he is off from having to take care of them so they are not in his mind.  We finally started the divorce paperwork and now all of a sudden he is calling to talk to them everyday, he is concerned over how often he sees them when normally he would take any chance possible not to see them, he is trying to take them overnight more and more when normally it is a hassle for him to.  why does it matter now?  Does he really think that doing that is going to make any difference in the divorce?  He still has to pay child support, he still has to split everything we own, he still has to help take care of them, why is he all of a sudden thinking and acting like the father he should be?  It is so insane, I just dont get it.