Responses
I think you mean this
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http://www.mangago.zone/read-manga/pretending_to_sleep_can_t_stop_him/
YES THAT'S THE ONE, THANK YOU SO MUCH!! ε=ε=(ノ≧∇≦)ノ
There's this girl and her sister is dating their childhood friend and the guy wanted to take revenge because of what they did to the guys sister in the past. The three of them live together for a bit and the fl did the deed with the sisters boyfriend infront of her sleeping. Please comment the link if you find it