it's not "Yul-A" it's really spelled as "Yul-ah" and your theory might be correct but you're wrong about the rape because I've read the raws and Yul's brother didn't even know they raped him 3 years ago until he got information about it, so Yul made his friends rape him cause he wanted to. Also about the rapping in the hallway was because Yul was upset and to get rid of his anger he took it upon Kyungsoo and was a coincidence that his brother and sister walked in on them (even though it's a hallway) inconclusion, Yul's an asshole and needs to jump off a cliff ( I applaud you for your theory though"
Thank you for your thoughts, especially if you've already read the raws :)
Still, it doesn't completely negate my theory. Even if Yul's brother hasn't known about the rape back then, Yul's motive of protecting Kyung could still be the same: He successfully made Kyung hate him and distance himself from Yul. In this scenario it wouldn't ever be possible for Kyung to come into the firing line of the brother - even if it means to destroy his own chance for happiness.
As for the rape in the hallway, I also wasn't too sure about that and just included this thought when I was proofreading my comment before posting, so I'm the least convinced of this particular part.
I'm not trying to invent a happy ending for Yul and Kyung, but for me, it's impossible to believe Yul did those horrible things simply 'because he wanted to'. And as a writer, I don't see any point in creating a protagonist (!) who's merely a rotten asshole to the core, so I feel the need to look for some reasoning behind his behavior. Especially since a 'savior' of Kyung is nowhere in sight, looking at the raws (which I can't read but still look at ^^"), so it probably won't be a protagonist1-makes-protagonist2-suffer-and-protagonist3-saves-him-from-his-misery kind of story. And the focus on Yul is too big to be a protagonist2-takes-revenge-for-protagonist1's-behavior-and-fucks-up-his-whole-life-like-an-awesome-savage kind of story. But that's just my two penny worth.
Read 23-58 & see if your hunch was right. https://webtoon.bamtoki.com/%ED%98%B8%EA%B5%AC-%ED%95%98%EA%B2%BD%EC%88%98
Spoiler warning (ch. 21 & 22)
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I can't help but feel like Yul-ah allowed the raping of Kyung-soo to protect him from his brother. Let me explain:
After the brother appeared, I had a hunch that he's someone really crazy and dangerous. In ch. 21, he warned Kyung about getting close to Yul and told him to leave him or else he'll regret it. In ch. 22, we were shown a flashback where he looked jealous of their mother's affection towards Yul - soon after that she's dead, probably 'fell' from the stairs. My assumption is that he's always been jealous over Yul (and still is) and thus, wants to destroy everything that makes him happy.
When Yul realized that his brother is well aware of his relationship with Kyung, he became afraid of what he might do to him, afraid that he might kill him - because he knows what his brother did to their mother.
So, to protect Kyung from his bastard of a brother, he let his friends rape the one person he's actually loved - to pretend-prove to his brother that Kyung means nothing to him, so it's not 'worth' hurting him.
Also, Yul was against bringing Kyung to their house because he knew he'd meet his brother there. And what did he do? He brutally raped Kyung in front of his brother's eyes - again, to prove Kyung's insignificance to him.
That, of course, doesn't make his actions right, but it's at least an explanation I could live with.