Impossible. You could never convince any animal to feel feelings it isn't designed to feel in the first place.

Yes... although it hasn't been the "official" system in all cultures, it has been in many, not just this one, and even in other cultures in which the official/standardized customs aren't set up that way and don't recognize it, the tendency still shows up: people picking a favorite from among their collection of mates, people leaving group arrangements or avoiding getting into them in the first place to be with an individual outside the group instead, people who could have multiple mates simply choosing to have only one instead, people feeling jealous if their mates seem to have others, and such.

Cultures reflect the nature of the species that created them; they didn't invent "stories" about people behaving in ways that people don't behave motivated by feelings that people don't feel. Stories that weren't based on the reality of who we are would not have been compelling stories and would not have convinced anybody that that's how it should be.