context: Dr. Stephen Fleming (Irons), a physician and Britain's Secretary of State for the Environment, leads a privileged life in London with his wife Ingrid (Richardson) and young daughter Sally (Gemma Clarke). Their adult son, Martyn (Graves), a rising young journalist, lives elsewhere in London. At a diplomatic reception, Stephen meets a young woman named Anna Barton (Binoche), the daughter of a British diplomat and Elizabeth Prideaux (Leslie Caron), her four-times married French mother who "lives in Palm Springs". Anna, who works in the arts and antiques department at Sotheby's auction house, introduces herself as a close friend of Martyn's but it is apparent that Stephen and Anna are instantly attracted to each other.
  A short time later Martyn brings Anna with him when he briefly drops by his parents sumptuous home to introduce her to his family and reveals that they are romantically involved. The developing sexual tension between Stephen and Anna becomes increasingly clear at this brief meeting although Martyn and his mother seem oblivious to this. Despite her relationship with Martyn, Anna arranges a tryst with Stephen at her small London town house. The following day, Martyn is appointed Deputy political Editor at his London-based national newspaper. Ingrid arranges a dinner to celebrate in London. While at dinner, Ingrid shows a distrust in Anna and asks her questions regarding her childhood. Anna expresses the loss of her brother who was a year older than her. He committed suicide when he was 16. When Ingrid asks why he killed himself, Anna replies, "Love." After dinner, Martyn drops off Anna and Stephen follows them. Once he leaves, Stephen talks to Anna about how much he "wanted to touch her during dinner." They have sex on the floor and in the bed. It is in bed that Anna describes in detail the suicide of her one year older brother at age 16 after he had expressed an incestuous desire for her, saying "he wanted me all to himself and not to grow up." She also describes that damaged people are dangerous and she hates a possessive relationship with anyone.
  Stephen's obsession with Anna deepens further and on a whim he leaves half way through a two-day European Parliament conference in Brussels to travel by train to Paris where Anna is spending the weekend with Martyn. While Martyn sleeps in their hotel room, Stephen and Anna have public sex in broad daylight in a church's open doorway as the church bell peals in the background. Afterwards Stephen checks into a hotel across the street from Anna and Martyn's, spying on the couple through his window. By then his infatuation has reached a point where he desires to be with Anna permanently, even at the risk of destroying his relationship with his son and family. In a meeting in a London park, however, Anna dissuades Stephen from doing this, assuring him that as long as she is with Martyn he will always have access to her.
  During a subsequent visit to Anna's home, Stephen finds that another man named Peter Wetzler (Peter Stormare) is already present and he tells Stephen that they are former lovers. A jealous Stephen initially assumes that Anna is cheating on him and, when Peter leaves, returns and confronts her. Anna denies being currently involved with Peter, and then She recounts that she had then immediately compulsively run to Peter and slept with him in order to grieve over her brother's death which she had witnessed. Stephen is placated by this explanation and the couple once again have sex.
  The Flemings travel to 'Hartley', the country estate of Ingrid's father, Edward Lloyd (Bannen), a retired but still well connected senior politician who has acted as Stephen's political mentor, to celebrate Ingrid's birthday. It is there that Martyn announces his engagement to Anna which visibly disturbs Stephen. That night, after Stephen receives oral sex from Anna, Sally observes him leaving Anna's room. After returning to London an anxious Stephen lies to Sally about what she saw, telling her that he was merely talking to Anna to try to "bring all the parties together" about the upcoming marriage because Ingrid was upset about it. Later the Flemings have an awkward lunch with Anna's mother, Elizabeth, who notices the strained behavior between Anna and Stephen. She correctly deduces that they are having an affair and, during a car ride with Stephen back to her hotel, warns him to put an end to it.
  Stephen initially complies and calls Anna to end their relationship. He tries to confess his misdeeds to both Martyn and Ingrid, but shies away from doing so both times. Stephen instead succumbs to temptation and phones Anna's home but hangs up saying nothing when Martyn (who is now living there with her) answers the phone. Anna then rents a small renovated flat and mails him keys where they can meet. She tells Stephen that she could not marry Martyn without being with him. They go to the flat at an appointed time and begin another raucous tryst, but Martyn â having been guided to the flat by chance â finds them in bed together. Stunned, he accidentally falls backwards over a stairway railing and plunges to his death. A devastated nude Stephen clutches Martyn's body while Anna silently leaves the scene.
  Stephen's affair is exposed and becomes the subject of a media frenzy, with a mob of reporters convening outside his house. Inside, an anguished Ingrid reacts to the day's events by questioning whether he had ever been in love with her and tells him that she wishes they had never met. "Everyone only has one person in life," she tell Stephen. "Mine was Martyn and yours was Anna."
  Now publicly disgraced, Stephen resigns his government position (he was to be appointed minister of health, therefore part of the cabinet) and seat in Commons. He meets Anna's mother at a hotel and finds that Anna is staying with her but they say nothing to each other as they meet for the last time. Stephen withdraws himself from public life and retires to an unknown location in Europe. In narration, he reveals that Anna now has a child with Peter. In his room he stares at a photo given to him by Martyn of himself with Anna and Martyn blown up to life size hanging on his wall.
question: Who does Stephen have an affair with?
answer: Anna