I recently finished reading Esther Perel's "Mating in Captivity" and her theory is very much like what you've said. Relationships may thrive on stability and knowing each other inside and out but eroticism is built on discovery and a bit of risk.

"Love rests on two pillars: surrender and autonomy. Our need for togetherness exists alongside our need for separateness. One does not exist without the other. With too much distance, there can be no connection. But too much merging eradicates the separateness of two distinct individuals. Then there is nothing more to transcend, no bridge to walk on, no one to visit on the other side, no other internal world to enter. When people become fused—when two become one—connection can no longer happen. There is no one to connect with. Thus separateness is a precondition for connection: this is the essential paradox of intimacy and sex."

Perel, Esther. Mating in Captivity (p. 48). HarperCollins. Kindle Edition.