After many lessons; the relationship between Sun and Jae Lee developed into an affair. The two were eventually found in bed together by Mr. Paik and the affair ended. Sun and Jin had been trying to conceive a child, but after visiting a fertility doctor, they were informed that Sun was unable to conceive due to severe endometriosis, causing more strain on the marriage. Later, however, the doctor confided in Sun that it was Jin who was infertile, and that he was afraid to tell him because of his job as an enforcer. Later, Sun learned of Jae Lee's death and attended his funeral. She asked her father if he would tell Jin about her affair, to which he declined, saying that it was not his place. During preparations for a business trip, with Jin, to Sydney and Los Angeles; Sun spoke privately with a woman acting as an interior decorator. Sun had planned to leave Jin and her family and the woman had helped Sun set up a false identity (and a place for her to hide until the search for her ended). She was given instructions to leave Jin at the Sydney airport at 11:15 precisely; a car would be waiting outside the Oceanic Airlines gate and she was to maintain a low profile.