Mind you the way it's written predisposes folx to sympathize with Taehon. (And dick gobbling as Sejun's immediate response is truly a bad/ridiculous writer decision please lol.) But what's not clicking? Taehon was involved in the murder of one parent and the permanent disabling of another even if it was as a helpless pawn. Is Sejun supposed to get over that in 5 minutes? Do your parents hate you that much that you can't figure out why Sejun is angry and thoughts of "he was a child" aren't particularly helpful in his processing of this traumatic reveal? Is it that difficult to discern how unmoored he feels in learning that the person who helped him escape his deceptive, manipulative cousin was also actively deceiving him in turn? (Which is why he has put things back on purely transactional terms.) That indeed he was connected to the circumstances that placed him in that abusive situation. From his pov this is a fucking horror show he can't escape. The writer isn't actually giving this development the weight it deserves...which is exactly why you're all annoyed and mad at Sejun (also you too are dick addled) so...nevermind. Carry on lol. Boo Sejun you hor. (●'◡'●)ノ
Love (that involves respect and trust) cannot be about lies, secrets and manipulation until you're forced to tell the truth. We understand why Taehon hid the truth from him but it was wrong. Period. He had time to tell Sejun the truth and he didn't because of his guilt over a terrible secret. He was a child then and a victim, yes. But so was Sejun. And as adults Taehon chose to treat Sejun as if he was still 5 so he could perform the rescue he couldn't then but in the process made Sejun a victim of others machinations and manipulations all over again.
He has every right to feel betrayed and to conclude that Taehon was only using him. If for nothing Sejun should have had the choice of deciding if he wanted to become this emotionally entangled with someone connected to the most traumatic, painful part of his life. I for sure wouldn't. There is not enough therapy money or good dick in the world.
(I mean OBV I want them to end up together. I am here for the fucked up storylines and over the top angst. But if Sejun heard this story and his reaction was "OMG, you really do love me. " I would have thought he was deaf or crack addled.)
Sir, you are very dunce. That's all I have to say.