From everything we've heard, it would appear that Casey was a lot more serious about the relationship with Tony than he was. He impresses me as being a young college kid, living for the present, with no thoughts of any long term relationship with a girl. Like most young twenty-somethings, he wasn't ready for any sort of commitment. During their brief relationship, Tony evidently stated that when he married and had children, he only wanted boys not girls. That statement alone could have been the catalyst for Caylee's demise.
While Casey was thinking in terms of a serious relationship and marriage, Tony was only thinking in terms of a brief fling.
edited to add (because I lost my train of thought)...............I thought Casey's reaction to Christina's honest emotion, incredibly cold and callus, a real indication of a heartless sociapath. There was also anger in Casey's reaction, as if she was angry that Caylee, and not her, was the focus. For Casey, that whole phone call had only one goal, and that was getting Tony's phone number. She needed to "set him straight" about what had happened.............Tony was much more important to her than the loss of Caylee.
