I just finished reading this and love it! In my mind I figured Maddie's attitude toward David and their "relationship" must have had something to do with her dealing with the loss of the baby. I think only a few months had passed between the beginning of Season 5 and the end. That is really not enough time for her to properly grieve and try to move on. For some people it might be, but maybe not for her. I think she was still unsure of what she wanted from David even before she lost the baby, and then after she was even more confused about what to do. Her not wanting him to give up on the family he so obviously wanted makes her selfless and goes along with her not wanting to change him in Season 4 by tying him down to her and the baby. Although, I do think she really should have given him the choice to make instead of making it for him. Sometimes people want to be with someone so much that they will sacrifice things to get that person. She thinks he wants a wife and baby more than he wants her, but maybe she's wrong?
But I really appreciate these stories that try to explain things that were missing from the show. I can't wait to read more!