The Patron Saint of Liars and Fakes
From Shousetsu Bang*Bang Wiki
The Patron Saint of Liars and Fakes is a story written by Hinotori. It ran in Issue 18 at http://s2b2.livejournal.com/104157.html, and is mirrored at http://www.shousetsubangbang.com/mirror/the-patron-saint-of-liars-and-fakes/.
Summary
From the author: "In which there is a bodyguard, fake boyfriends, an undercover agent and amnesia."
From delicious.com: "Adam is assigned to investigate Benedict Horton, and does so by disguising as his personal bodyguard/fake boyfriend."