"I want the second kiss, the thousandth. Tell me what it’s like after the toxic rush of the first is gone, and you have imprinted each other, skin on skin on skin, until the memories have smeared into each other."

Not fiction, but stick with me here. Douglas Hofstadter, in I Am a Strange Loop, describes how, over the course of years, his wife came to inhabit his brain. He thinks of it as a model of her, a copy, that is so detailed he can have conversations with it. After his wife died, he continued to talk to the model in his brain and have a marital relationship with it, in terms of making decisions about how to raise their children and such.

Closest analogy I could get to what you describe.