The Backstory of Jung Se-yeon: The mystery behind Su-ho and Seo-jun’s rift centers on Se-yeon's suicide. Se-yeon was framed in an industry scandal by Su-ho’s father’s agency. When Se-yeon called Su-ho for help, Su-ho was in shock over catching his father with another woman and did not answer, fueling years of self-loathing and Seo-jun's resentment.
Kang Su-jin's Downward Spiral: Tormented by an abusive father who physically punished her for losing top academic marks, Su-jin grows jealous of Ju-kyung’s loving family and Su-ho's affection. She leaks Ju-kyung's old middle school photos online, betraying her closest friend before being exposed and transferring away.
The Two-Year Time Jump: In Episode 14/15, Su-ho’s father suffers a sudden brain hemorrhage in the United States. Su-ho flies to America, and amidst prolonged medical uncertainty, breaks up with Ju-kyung so she isn't held back. Over these two years, Seo-jun remains by Ju-kyung's side, eventually confessing his love.
The Resolution: Realizing Ju-kyung’s heart still belongs to Su-ho, Seo-jun lies to her that Su-ho is returning to America, sending her to Prince Comics where the main couple tearfully reunites. Seo-jun debuts as an idol performing Se-yeon’s final written song, releasing his past grief. Su-jin returns reformed, apologizing to Ju-kyung. Ju-kyung achieves success as a professional makeup artist, confident in her bare skin.