YOU SAID:
i've heard he's been sleeping with your sister
INTO JAPANESE
彼はあなたの妹と寝ていると聞いた
BACK INTO ENGLISH
I heard he slept with your sister
INTO JAPANESE
彼はあなたの妹と寝たと聞きました
BACK INTO ENGLISH
I heard he slept with your sister
Come on, you can do better than that.