Abbie and Dexter

Can someone explain this relationship to me? What is it that he wants from her? It's like this mother/son Freudian romance. He really seems to want to open up to her, and near the end, where he gives her a photo of his family, he leans on her like he thinks he can find some kind of solace in her. But why her? What's the deal? Doesn't he see that she's too emotionally unavailable to really give him comfort? It was really well acted, though --- I felt his desperation.