Why Does My Brain Still Think I Need Him?

Oh, I think that something must be array in my brain somewhere, somehow because I just feel like there are days that I can't help but wonder about him. We had many years together and even though we went through many very bad days, we also had some good days there too. He cheated on me, so that's that. He made his decision when he made the decision to cheat. Obviously he was more into "her" than he was into "us" and our family. Things are done now, and there's nothing that I can do about it. However, since we do have a child together and she is still under 18, I have times that I feel we need to talk about her and how she is doing. Well, that's not happening these days because he just flat out doesn't answer his phone at all. I have tried calling at different times, using different phone numbers, even leaving messages to no avail. I don't understand him or what he's thinking. Does he think that just because we are apart now that he doesn't have to worry about his daughter? It kind of seems as though he has forgotten that he still has an obligation. What is he thinking? And why does my brain still think that I need him to even care?