Kyuuso wa Cheese no Yume wo Miru

Ootomo Kyoichi, a weak-willed salaryman in a troubled marriage, is cheating on his wife. To his surprise, his wife hires a private eye to expose his affair - and the private eye is none other than Imagase, an underclassman Kyoichi knew in college. Imagase explains that he's gay and always had a crush on Kyoichi, so he offers to hide the infidelity in exchange for the make-out session he'd always fantasized about back in college. Kyoichi reluctantly agrees, thinking it will save his marriage, but things with Imagase soon spiral out of control.
(Source: Seven Seas Entertainment)
Note: Includes two extra chapters, with one first released in the 2009 edition.