I could see a poly ending only if the author goes full hentai and has Nanase schlicking to thoughts of the scene in front of her and having a sexual awakening lmao. However, it seems like the author is trying to maintain a somewhat serious plot, even if all the characters are behaving in unbelievable ways.
Beyond that, I'm most curious about whether Nanase's friend hits the rebound. It's very clear that she's the only person who actually cares about Nanase lol, and the opportunity is now there.