He told TV Guide that there is "quality storytelling to be had" after the pair (played by Nathan Fillion and Stana Katic) admit their feelings for each other.
"Everybody talks about the Moonlighting curse," he said. "[But] anybody who's been in a relationship knows that they have complexities and compromises. There's plenty of stuff to mine."
Marlowe also argued that having the characters refuse to discuss their recent kiss is not "a cheat at all".
"To confront the kiss head-on wouldn't be true to either of the characters," he suggested. "She's never been open about how she feels about anything, and he usually finds a way to joke about everything. By not doing that, you understand how important it really was to him."
Castle airs on Mondays at 10/9c on ABC.