Bittersour

Ji-Won is having a happy time with the man who came over for a one-night stand when he hears arguing coming from the next door. Ji-Won brushes it off as no big deal, but when the sound of someone drunk singing breakup songs echoes all night starting the next day, he can't take it anymore and goes over to the next door. There, Ji-Won sees Hyeon watching the video of his singing contest performance—a moment that became his embarrassing past. When the man from the video suddenly shows up, Hyeon is startled out of his wits...

(Source: Lezhin, translated)