Something to think about for a second as well. Imagine you and your friend decided to swap girlfriends for a double date, but everyone agreed to keep things strictly non-sexual. No kissing, grouping, touching, or fucking outside what you might do with a regular friend. You are just swapping partners for a date night. You each take the other's girl out for dinner and dancing just as you would on any other date with a girl. In this sense, it's sharing your partner romantically, but not sexually even though everyone's loyalty is to their own partners. It's kind of the other side of sharing where instead of sharing the sex component of your relationship with your partner, you share the romantic component instead. As far as my understanding of NTS/sharing/swinging goes, date night partner swapping like that would still be included just as much as if it were just "let's fuck each other's girl for just one night!"
I do agree that whatever relationship is between everyone, I don't think there will really be anything romantic really with other people. I'd imagine it'll turn out that MC and Ayumi's relationship with their friends will simply turn into a friends-with-benefits for some hot kinky sex. I get the feeling that Terracce and Ari won't be the only people they end up bringing into their bed before all is said and done.
