From Seven Seas Entertainment:

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.

Note: “Hummingbird Rhapsody”, an extra chapter involving Imagase's past, was released in the March 2020 issue of Flowers magazine. Revised chapters of the manga began publication in this issue as well.