Otonage

From Fantasyshrine:

Up and coming interior planner, Takamori Fumito, is having an affair with Eto Shunsuke, the president of the company where he is working, despite the fact that Eto is married to an owner of a famous fashion apparel. From the very beginning, they made it quite clear that their relationship is strictly physical. However, Takamori realizes his heart is now in danger— a story about adults struggling with love and sex.