Louis Malle - Damage (1992)

A member of Parliament (Irons) falls passionately in love with his son's fiancée. They pursue their affair with obsessive abandon despite the dangers of discovery and what it would do to his complacent life and his son. Completely obsessed, he wants to give up his current lifestyle to be with her. She has no intention of allowing him to do this, preferring to have her marriage to the son as a cover. They are eventually discovered, and must deal with the damage. Based on the novel by Josephine Hart.