Responses
This is the one I believe.
http://www.mangago.zone/read-manga/koakuma_no_sanctuary/
Thank you so much!!!! I've been trying to find it for forever.
No problem :)
This happened at the end of the manga after each couples story is told.
There were several couples (I think 4). One of the couples was a model (uke, I think his name started with an L) and the president of a company. One of people was an artist or something.
All of the people met up at an art show (their stories are connected), but each couple didn't know about the other couples. So after the art reception, they all went out to drink, and each couple sat next to each other. Then one of the people commented on how everyone sat with someone that should be strangers (now it's reveal that everyone was sitting with their lovers).
And it ends with each couple having sex (except one).
So basically it's a mash-up of all 4 couples. I think it all happens in the same manga.