You Just Might Get It
From Shousetsu Bang*Bang Wiki
You Just Might Get It is a story written by juou no zen. It originally ran in Yes, And 3 at http://s2b2.livejournal.com/312773.html, and is mirrored at http://www.shousetsubangbang.com/mirror/you-just-might-get-it/.
Summary
From http://fairyninjas.wordpress.com/2015/07/21/circus-maximus-ssbb-yes-and-3/: "A couple goes to dinner with the wife’s old girlfriend, and then two of them end up acting out the fantasies of the third. I might say this was the hottest of the bunch, even if I’m not usually into the ladies."