Debra being in love with Dexter was taboo. Dexter is shocked by her statement. Debra herself is shocked by these feelings and her dreams.
She tells him “ you’re a serial killer and I’m more fkd up than you!”
The idea behind this “twist” was to help make Debra more ambivalent about the “right” thing to do about Dexter and his hobby.
That’s an amazing memory I just watched the im more fucked up than you line