Originally Posted by
Gilly
LSI
His "code" is made of personally tailored maxims to guide his behavior and perpetuate his survival, not philosophical or sociological treatises. His blatantly EIE sister Deb is his dual, she sheds the light of vulnerability and Fe and genuineness that his work is laid out to perpetuate; the theme of the story is essentially Dexter creating a safe world for Deb, or at least people like her: innocent in spirit, driven to do good, incorruptible, whereas he is the opposite of all of these. She is the only one who can bring things into perspective for him; her existence justifies his (and, ironically, vice versa). She is his dual.
Rita was his super ego, EII. Everything that he thought he should have; every word she spoke was what he knew was right but his very being rebelled against. Stability, peace, trust...all things counter to his nature which he thought he should aspire to, because he assumes that since he is evil, the opposite of what he wants must be right. And for fooling himself, he is held responsible for her death, if not by the law then by his own conscience and, symbolically, in the eyes of Astor.
Trinity, LSE, was his contrary, appearing to be like Dexter on the surface, but conducting his life in much the opposite fashion.