"It was to good to be true" || Sakuatsu ||

Sakusa and Atsumu get married a few years after highschool, and no one seemed to ever know Kiyoomi other than Atsumu. Although Atsumu has many memories, and even is engaged to Kiyoomi. Everyone always asked who Kiyoomi was. Never brought up any old memories, even Komori. His own cousin. What is going on? Why was everyone telling Atsumu it was his imagination?