This is a remake of the 1949 Columbia film, The Reckless Moment, starring Joan Bennett and James Mason, directed by Max Ophuls. Both films were based on the story "The Blank Wall" by Elisabeth Sanxay Holding.
The trivia item below may give away important plot points.
The sex tape footage could not be shot until actor Jonathan Tucker had turned 18. According to one of the directors, it was actually shot on his birthday, and he kept calling his girlfriend between takes.