YOU SAID:
The cat was sad when he was at my house
INTO JAPANESE
彼が私の家にいたとき、猫は悲しかった
BACK INTO ENGLISH
The cat was sad when he was at my house
INTO JAPANESE
彼が私の家にいたとき、猫は悲しかった
BACK INTO ENGLISH
The cat was sad when he was at my house
That didn't even make that much sense in English.