Miwaku no Hitori Zuma

Our nerdy hero has a dream... It must be a dream; real life just isn't this easy!
One day, he finds that a young, beautiful married woman has moved in next door. Full of curiosity, he tries to eavesdrop on her activities through the wall... When he hears her erotic moaning, he realizes she's masturbating! A young, beautiful wife masturbating inches away from him... Our hero quickly loses patience and begins to peep in...

[From Gamelex]