YOU SAID:
stacy slept with a dog
INTO JAPANESE
ステイシーは犬と一緒に寝ていた
BACK INTO ENGLISH
Stacy was sleeping with her dog
INTO JAPANESE
ステイシーは犬と一緒に寝ていました
BACK INTO ENGLISH
Stacy was sleeping with her dog
That didn't even make that much sense in English.