Yeah, but he only did that because his mind was already fucked up, the brother kept leaving "suggestions" behind before turning off the hypnosis (making him think about him instead of sunbae when he get aroused etc) to the point he simple didn't need the hypnosis anymore, MC body is used to him, and his mind is pretty much melted, so he just convinced him is normal for bothers to relieve each other and he went along with it
(Keep notice that the MC is always questioning himself of why he's doing it, and how the bother keep insisting on the idea that this is what they need to do so "they can get along with each other", MC is brainwashed, brother knows and wants to keep that way)
Just saw this again and it has wrong grammar.... I am not blaming him or anything... I was just answering the comment... "isn't he still under hypnosis?"... Me blaming him means I didn't read the manhwa from the top... I've seen the process of hypnosis and now even without the word you can't say he isn't under one at all.
Bro you're literally cheating on your boyfriend rn