The fidelity question is difficult for me. Society has made us believe we're supposed to be monogamous when we're not killer whales, or whatever the monogamous species is.
Imagination, it turns out, is a great deal like reporting in your own head. Here is a paradox of fiction-writing. You are crafting something from nothing, which means, in one sense, that none of it is true. Yet in the writing, and perhaps in the reading, some of a character's actions or lines are truer than others.