Why would anyone choose an XXUX exclusive relationship over traditional monogamy? The answer lies in three psychological shifts.

We aren’t talking about standard monogamy. We are talking about a fortress of two. From the obsessive devotion in Twilight to the "ride or die" chaos of Mr. & Mrs. Smith and the possessive romance of K-dramas like The Glory , the XXUX storyline is dominating fanfiction archives and bestseller lists.