Anyways what I previously commented and "bergil" also pointed this out is that this story, without understanding the dialogue, seems very similar to "Karami Zakari" (which even has a real-life porn version lol) whereby the MC and his crush get dragged into swinging and has to watch his crush getting screwed.
There is also another Hentai called "Chitose" with a similar concept. Seems to me that this might be a new Trend in NTR.