I remember this movie where a couple hire an asian girl as help and they end up falling in love with her. The make an agreement to share the asian girls affections and start cheating behind their back to spent more time with the girl. They actually dope themselves at night with laudanum to avoid cheat on each other with the asian girl. When the girl abandon the couple the relationship crash.

I saw it 1980-1988 on cable TV pay channel (the movie has a lot of sex /erotic scenes) on it.