Help!!!

I read a yaoi manga a long time ago where 2 office workers who were dating got caught by another guy and the guy said if they didn't want him to tell everyone they had to let him watch or do a 3p or something and they did and bottom saw the top getting topped by the other dude and he wanted to top and the next day he said he wanted to see the top get topped by the other guy and the other guy said they can share him.

I dont remember if it was a side story or a main story. Please help.