Responses
Spoiler
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Without govojg away too much, no, he didnt sleep with his dad. Yujin was drugged with heat inducers and made to believe the dad was Winston. Yujin got dragged into bed (honestly, the translation of how he got into bed is a little off. Yujin says in one chapter he doesn't remember anything after the tea but waking up in a motel but another chapter, he remembers following Winston's scent, same scent as his father, into the room). Nothing happens with the dad though.
Tysm
Someone spoil what happened with the dad (assuming it's a misunderstanding) or did he actually cheat with the dad?