{{I=1x08SawyerJessica.jpeg=right=200=Sawyer sleeps with Jessica, a married woman {{Crossref}}}}
Many characters have had '''affairs''' on ''Lost''. These affairs are generally kept character secrets from the person's spouse, and are a great cause of internal and external conflict for the characters on the Island. 

==Significant affairs==
===Sun and Jae Lee===
{{I=Ep3x02-jae-sun.jpg=left=200=Sun's affair with Jae Lee {{Crossref}}}}
Due to the controlling and domineering nature of her husband Jin, Sun Kwon engaged in an affair with Jae Lee, a man whom she had met before her marriage to Jin. The affair was soon discovered by Mr. Paik, Sun's father, who chastised his daughter for the shame she had caused him after he walked in on Sun and Jae Lee. Paik, without Sun's knowledge, contacted Jin to kill Lee, though he did not reveal the affair. Though Jin severely beat Lee, he could not bring himself to kill him, instead warning him to leave Korea and go to America. Lee, believing that the affair had been discovered, instead committed life and death by jumping out of his hotel window and landing on Jin's automobiles. At Lee's funeral, Paik confronted Sun, who was watching from afar. When questioned by Sun on whether or not he would inform Jin of the affair, he told her that it was not his place to do so. {{Crossref}}

Several weeks after crashing on the Island, Sun discovered that she was pregnant. Due to the fact that Jin was infertile, she worried that the baby might have been Jae Lee's. {{Crossref}} However, after a trip to the Staff with Juliet, she discovered that the baby did indeed belong to Jin, easing her worry. {{Crossref}} {{I=Jin forgives Sun.jpg=right=200=Jin forgives Sun for the affair {{Crossref}}}} 

Several weeks later, after the arrival of the science team onto the Island, Sun, frustrated with the lack of answers she had been receiving, convinced Jin to accompany her in joining survivor factions's group. However, Juliet found out of her plans, and warned her that she would die in childbirth on the Island. Sun, however, did not heed Juliet's warnings, forcing Juliet to reveal Sun's affair to Jin in a last-ditch effort to get Sun to stay. Jin, hurt and angered, left to go on a fishing trip with Bernard, who restores Jin's faith in Sun through a conversation about marriage. Jin returned, forgiving Sun for the affair and showing that he was willing to start fresh. {{crossref}}

===Juliet and Goodwin===
{{I=Juliet and Goodwin.jpg=left=200=Juliet and Goodwin kissing {{Crossref}}}}
Soon after her arrival on the Island, Juliet Burke struck up a friendship with Goodwin Stanhope, a fellow Other whom she first got to know by treating his chemical burn. The relationship between them soon evolved to something further, even though Goodwin was married to Harper, the Others' therapist. Benjamin Linus, who coveted Juliet, became suspicious of the affair after witnessing very friendly relations between Goodwin and Juliet. {{crossref}}

Harper soon discovered the affair, and confronted Juliet about it during a therapy session, telling her that she followed Goodwin and witnessed him and Juliet having sex. Harper warned Juliet that if the affair continued, there would be consequences, though not from her. She revealed that Ben, in his jealousy, might react extremely. {{Crossref}}

Harper's suspicions were proven to be correct when, on September 22, 2004, Ben sent Goodwin to the tail section of Oceanic Flight 815 to create a list of survivors and to monitor them. Ben, aware that mission would be dangerous and possibly fatal, learned of Goodwin's death several weeks later due to impalement by Ana Lucia Cortez. He then took Juliet to see Goodwin's corpse, revealing that he had indeed planned Goodwin's death because he believed that Juliet belonged to him. {{Crossref}}

===Sarah Shephard and an Sarah Shephard's lover===
{{I=2X11-SarahJack.jpg=right=200=Sarah leaves Jack {{crossref}}}}
Frustrated by her Jack Shephard's need to fix everything, Sarah Shephard began having an affair with an Sarah Shephard's lover. The affair remained secret from Jack until he revealed to Sarah that he had kissed Gabriela Busoni after the death of Gabriela's Angelo Busoni, prompting Sarah to tell Jack that she had been unfaithful as well, and was in fact leaving Jack, leaving him heartbroken. {{Crossref}}

Jack became obsessed with discovering the identity of Sarah's lover, going so far as to begin stalking her in an attempt to find out who it was. He became increasingly paranoid, eventually believing her lover to be his own father, Christian Shephard, after finding Christian's name in Sarah's phone. Jack went so far as to publicly confront his father at an Alcoholics Anonymous meeting, eventually assaulting him. Sarah bailed Jack out of jail, but told him that Christian had only been calling her because he was worried about Jack. When Jack asked her who her lover was, she simply told him that "it doesn't matter who he is, it just matters who you're not." {{Crossref}}
 {{I=Sarahpregnant.jpg=left=200=Sarah pregnant with her lover's baby {{Crossref}}}} 

During his time spent incarcerated with the Others, Jack asked Juliet if his wife was truly happy with her lover, to which Juliet replied that she was. {{crossref}} After being rescued from the Island, Jack rescued a woman from a car crash and was taken to the emergency room, where he was met by Sarah, who was still his emergency contact. Sarah, visibly pregnant, refused Jack a ride home. {{Crossref}}

==Other affairs==
*Mary Ford had an affair with Anthony Cooper while married to Mr. Ford, and Cooper conned her out of $38,000, causing Mr. Ford to kill Mary and himself. A young James Ford hid under the bed as this occurred. {{crossref}} {{crossref}}
*Diane Janssen had an affair with Wayne Janssen and became pregnant with Kate.  She was in a relationship with Sam Austen at the time, but he was away on military service.  {{crossref}}
* Christian Shephard had an affair with Carole Littleton, while married to Margo Shephard. This resulted in the birth of Claire Littleton. {{Crossref}}
* Jessica had an affair with James "Sawyer" Ford(Jessica's husband). {{crossref}}
* Susan Lloyd had an affair with Brian Porter while she was in a long-distance relationship with Michael Dawson. This later led to Brian taking custody of Michael and Susan's son, Walt. {{Crossref}}
* Nikki Fernandez had an affair with Paulo while she was dating Howard L. Zukerman. She engineered the affair as part of a plan to steal Zukerman's diamonds. {{Crossref}} 
*Sun came very close to having an affair with Michael on the island, while married to Jin. {{crossref}}
*Jack came very close to having an affair with Gabriela Busoni after the death of Angelo Busoni. He was still married to Sarah at the time. {{Crossref}}

* Claire and Kate are both products of extramarital affairs.

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