Lost season 1 hinted at a love triangle that was all but confirmed as part of Lost: Missing Pieces, but the series thankfully ignored it after this and avoided ruining its best characters: Sun-Hwa Kwon and Jin-Soo Kwon. Co-creators Damon Lindelof and Carlton Cuse created Lost: Missing Pieces, a collection of 13 webisodes (or mobisodes, as they were marketed by Verizon Wireless who originally released them). They were short episodes, formatted primarily for mobile devices, following famous Lost characters such as Jack Shepherd, Kate Austen, and Ben Linus. However, the eighth mobisode, "Buried Secrets" nearly undermined one of the best arcs on the show and ruined a beloved relationship forever by confirming an awkward love triangle.
When Lost began, Jin and Sun (Daniel Dae Kim and Yunjin Kim) had a rocky relationship. The South Korean couple appeared to not speak English and could not communicate with the rest of the survivors. Jin was fiercely protective of Sun and even beat Michael Dawson (Harold Perrineau) in front of his son, Walt, for apparently stealing Jin's watch. Michael then became somewhat close to Sun, eventually finding out that she could speak fluent English (which even Jin did not know, let alone the Oceanic 815 survivors). The mobisode showed them almost kissing before being interrupted. Feeling betrayed by Sun but also ashamed of how abusive he had become after working for her corrupt father, Jin joined Michael as well as Walt and James "Sawyer" Ford on the raft to try and find salvation at the end of season 1. He was eventually redeemed and rekindled his relationship with his wife.
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While an affair between Michael and Sun was hinted at in season 1, it would have completely undermined Sun's journey in the long run. Sun-Hwa Kwon and Jin had a complicated backstory defined by corporate corruption, a desire to act honorably, and immense marital strain. Lost's magical island eventually proved to Jin how strong his wife was, leading him to recognize how toxic he was being by disallowing her from being her true self. This would have been undermined if Michael had been a "savior" of sorts, suggesting that Sun needed a man to save her from another man.
Jin began Lost as one of its most unlikable characters, far different from the lovable likes of Hugo "Hurley" Reyes and Charlie Pace. However, his redemption and desire to change his ways and save his marriage was one of the show's best storylines. Jin and Sun felt like real people with real problems. If the show had gone even one step further than the almost kiss of "Buried Secrets", Jin's redemption and genuine romance with Sun would have been ruined by a tacky island love triangle story.
The storyline would also not fit in with Michael Dawson's narrative journey. Michael was always obsessed with getting his supernaturally gifted son, Walt, off of the magical island. This took him to a very dark place and even saw him kill two of the survivors, Anna-Lucia and Libby and strike a deal with Ben Linus, leader of the Others. A love triangle storyline would only distract from his compelling journey. Lost was wise to discard a Sun and Michael affair after season 1, but "Buried Secrets" was a reminder of how the beautiful romance of Jin and Sun could have been ruined forever by a clumsy affair.