Io so che tu sai che io so (1982)

Fabio Bonetti has been married to Livia for almost 20 years. One day a private eye investigating on their neighbors, the Vitali family, by mistake starts filming and recording Livia's life. When Fabio gets the films he discovers his family life is far from being tedious and flat. Livia cheats on him, and their daughter Veronica is a drug addict. He is also under the threat of a terrible illness. Maybe Fabio will start considering a new life style.