Siwoo was a witness to how Dohyeok treated Suha, how he hurt him and obviously tortured him by forcing Suha into a 3some. Without realizing it Siwoo had hated Dohyeok deeply and cursed him. Especially when Dohyeok started to like SIwoo and did extreme ways just so that Siwoo would not leave his side, it made SIwoo hate him even more. it's right that the author doesn't make them a couple. their relationship is a hell that makes them hurt each other.
Translated with DeepL.com (free version)
The stories about a rich kid have a roommate and grow up together. The friend love to write and his dreams to become a novelist. But there's a earthquake and the rich kid always come to search for his friend but there's nothing to found. Few years later, he found out the friend is still alive and gonna marry his lady savior. The rich kid himself have a fiancee but never put a date of marriage. He said why not me, after the years I'm searching for you. Later they confessed each other and choose to cut out the marriage and stay together until they old
i volunteered for the money, papa