YOU SAID:
I was delighted to sleep with your mother last night
INTO JAPANESE
昨夜お母さんと一緒に寝てよかったです
BACK INTO ENGLISH
I'm glad I slept with my mom last night
INTO JAPANESE
昨夜お母さんと一緒に寝てよかった
BACK INTO ENGLISH
I'm glad I slept with my mom last night
That didn't even make that much sense in English.