Hitozuma Yuzuki-san no Fudeoroshi Lesson ~Hajimete na no ni Konna ni Ippai Dashite... Ikenai Ko ne~

The main character is a student who never had a girlfriend.
He's been secretly in love with Yuzuki who lives the next door.
He gets excited when he finds her underwear when invited to her house.
Yuzuki, who was feeling lonely offers an affair with him.
And this is the beginning of their secret love affair!

[From DLsite English]