@Siikalahna Dan-I probably doesn't notice because Ru-Da never acts this way in front of Dan-I and no one tells her when he does. It's literally not her fault for not knowing that someone she views a friend is a two-faced manipulative asshole with a worrying possessive streak a mile fucking wide when said friend goes to great lengths - like letting himself get hurt - to stay on her good side and the people who see what he's like won't tell her.
Even if you want to disregard all that, she's a fucking
child. She's 15-16 years old, and she's known this kid for literally a
month. Cut her some fucking slack.
Additionally, Ru-Da was likely put in the story as a means of progressing the plot. How? I don't know yet, and yeah, there's probably an element of a love triangle
there partially for the fucking drama of it, which, yes, is annoying, and partially because, in my experience, a lot of Korean romances have love triangles. Or maybe it's yet another trope that the author's including. In any case, Dan-I
hasn't lost "all her brain cells," she's just put her guard down around Ru-Da and is operating under the assumption that Ru-Da's a girl, which, yes, is ridiculous, but so is every other fucking trope that's being parodied, and which
does change how she views Ru-Da's actions. Case in point: Yeoryeong.
Lastly, if possible, please remove your use of the word "r******d," as it's an outdated and incredibly offensive word that has been unfairly used in reference to people with developmental disabilities and others. "Cunt" has also technically been used derogatorily against women, especially in the US, but that isn't as bad, I think, given some movements of feminists to reclaim it.
And please use their names. Presumably, you've read all 62 chapters of this, so by this point, even if you don't know how to spell them, which is fair because I also had to go back to double-check my spelling, you should at least know them by now, if not recognize them.