The original source material is a mature manga series. You can find official digital versions and chapter updates on Coolmic , which often licenses these types of romance and mature titles.
The story centers around two married couples who have been close friends for many years: the (Koushirou and Kanoko) and the Mameda couple (Asahi and Natsume). They are neighbors and spend a significant amount of time together, trusting one another implicitly. read fuufu koukan modorenai yoru link