Inkya no Ore ga Sekigae de S-kyuu Bishoujo ni Kakomaretara Himitsu no Kankei ga Hajimatta.

My peaceful school life... is officially over. Izumiya Ryouta, an introverted otaku, suddenly finds himself surrounded by the top three beauties of the class after a seat change. In front of him sits the little-sister-type Miyama Airi. To his left, the cool and detached gyaru, Ichinose Yuria. And to his right, the refined, black-haired class rep, Kuroki Ruri. On the surface, they're flawless beauties—but Ryouta stumbles upon secrets that none of them can ever let out... "P-Please...! Just don't tell anyone about this!" "From now on, we're in that kind of relationship." "This is a secret... just between you and me, Ryouta-kun." All he wanted was a quiet otaku life—so how did things end up like this?! Caught between three troublesome girls, an introverted otaku desperately fights to avoid any more chaos in this love-comedy showdown! (Source: Kadokawa, translated)