Once días, once noches

I first watched this movie on cable back in the late 80s and 90s. They would show it regularly; I didn't know who directed it until a commentator mentioned Joe D'Amato's name who died in 1999; The film is about a guy named Michael marrying this ordinary woman named Helen; He hooks up with this woman Sarah, who he doesn't know is writing a book of men's sexual natures, and he just happens to be No 100; What turns into an full-fledged blown out affair for Michael and Sarah turns into pure agony for poor Helen who is waiting for her day at the altar; The ending can be predictable to some; But it's worth a look; It's hard to get this movie here in the US but I am sure they still show on the premium cable channels;