Indeed, the romance myth is focused on scarcity: There is only one person out there for you!!! You need to find someone to marry before you get too old!!!! The sexual exclusivity rule is focused on scarcity, too: Each person only has a certain amount of attention or attraction or love or interest, and if any of it goes to someone besides their partner their partner must lose out. We don’t generally apply this rule to other relationships—we don’t assume that having two kids means loving the first one less or not at all, or having more than one friend means being a bad or fake or less interested friend to our other friends. We apply this particular understanding of scarcity to romance and love, and most of us internalize that feeling of scarcity pretty deeply.