Michael C. Hall comments on the Debra/Dexter stuff:
“[It wasn't] without our blessing. Jennifer and I were aware that the story was moving in this direction. We laugh about it, we shake our heads … but you know, in as much as there are inevitable parallels, we’re both very professional and committed to telling this story.
And frankly, whatever’s happened with Jennifer and me and our relationship’s evolution notwithstanding, Dexter in the first episode says, “If I could ever have feelings for anyone, I’d have them for Deb.” I think those two characters have been on some kind of collision course from the get-go.
In t he part I bolded I think Dexter meant human feelings in general and not the falling in love kind. Early on Dexter was portrayed as someone who had no real human feelings of any kind.