I read at this page
https://chrysanthemumgarden.com/novel-tl/at/
here ya go mate have a nice reading
True. calling him a black flag is too much lol. i have high standards for ML, and rarely tolerate toxic behavior, but in Dohyun's case, i understand the reason behind his mistakes. He also never treated Wooyeon badly, in fact he really cared for him.
a little bit Spoiler below:
Dohyun knew from the start that what he did was wrong, but was too afraid to say it because he was worried about Wooyeon's reaction (he was wrong for this, but i understand). He never intentionally wanted to hurt Wooyeon.
As someone who has finished the Novel, I can assure you that Dohyun is not a red/black flag, and his mistake is not as bad as the spoilers out there. This is why you should read the novel until the end idk why they called him manipulative but i never find that side of him in the novel, he never gashlight Wooyeon or anything. He aplogize properly. And his POV is soo funny and sad at the same time...