Nagasare Tsuma no NTR Monogatari ~Gitei to Otto no Shinyuu to Furin no Yuuwaku!?

It's been over two years since Rin married her husband Toake Tatsuomi. With Tatsuomi's parents having passed away early, they live together with Tatsuomi's younger brother Kousuke. With their moments of love at night already having dwindled to nothing, it's a lonely everyday life for a woman in her prime. On the eve of their third wedding anniversary, Tatsuomi decides to go on a long business trip. This is also when she receives a business card from Torai Byakuya, Kousuke's homeroom teacher and Tatsuomi's close friend, with his phone number written on it. [Translated from DLsite]