Following the death of Rita, Dexter realizes a bit too late how much he truly loves her. In a flashback sequence, we see the couple's first date, which occurred at some point before the events in the 1st season. Apparently, Dexter's sister Debra arranged the occasion, and while out for an evening of romance, Dexter takes the opportunity to continue his dirty work as a serial killing obsessive. After all, he hardly knows Rita all that well, and making attachments proves to be fairly difficult for him — he simply goes going through the motions in an effort to appear normal. If only he knew that it'd lead to the best relationship he could've ever hoped to have, as well as the birth of his son.
In the flashback, Dexter excuses himself to follow a gentleman he is targeting. Promptly, he plunges the needle into his target and manages to place the unconscious man in his car without being seen. Of course, the event was entirely premeditated, and Dexter selected the restaurant for strategic purposes. Rita, none the wiser, has no clue what Dexter is up to and only hopes to get to know him personally. Painfully, Dexter cuts the date short with a feigned excuse. While a beloved character in the eyes of many, it's obvious that Dexter didn't deserve Rita. Not only that, but this retrospective replay in his mind might have sparked a tinge of regret and pushed him to come to the same conclusion.
