Tomodachi no Mama to, ~Hirusagari no Eroero Kozukuri Lesson

This story is about Keigo, a boy whose class thinks of as 'the cute boy.' But for as long as Keigo can remember he's had a crush on his best friend Yukito's mother, Aya. One day Keigo comes to play at Yukito's house and suddenly gets a lot closer to Aya. "Keigo-kun, I'll teach you everything. E-V-E-R-Y-thing."

[edited from DLsite English]