Responses
Doushitemo Furetakunai _is_ the original story. The side stories about second couple - Deguchi and Onoda - were doujinshis (Doushitemo Furetakunai dj - After 10 Hour; Doushitemo Furetakunai dj - After 9 Hours; Doushitemo Furetakunai dj - The World with Color), here included from chapter 7. AFAIK, Soredemo Yasashii Koi wo Suru and Yasahii Uso wa Minoranai were stand alone stories about Deguchi and Onoda and along with djs were collected in http://www.mangago.zone/read-manga/soredemo_yasashii_koi_o_suru/
Oh thanks
Wait a minute, since Sensei Said this is Doujinshi then what's the original story?