Judging by Saebyeok's previous performances, he won't be able to speak his mind and tell Gwangchae the truth about that night nor that he really likes her, they will break up and Saebyeok will continue to lead his pitiful, lonely, bullied and insignificant existence. I doubt it will affect Gwangchae at all since she's never shown any romantic interest in Saebyeok nor ever acted like a real girlfriend but instead only acted like a casual acquaintance.
It's such a classic route and we've seen it coming but idk man I found really funny, and I never find this trope amusing but idk man lmao. Thanks for the update!