Joku Doreizuma ~Musuko no Tomodachi ni Okasaretsuzuketa Mikkakan~

Iori Oku, a main character, comes home from his lesson early and finds his mother and his best friend having aggressive sex on bed.
"I want to do the same thing ..."
As he thinks, he imagines Chiaki Iwane, his best friend's mother.
He was always having a feeling of pale love toward Chiaki.
As he finds his desire, his deep sensual summer starts.

[From DLsite English]