since in the flashbacks we're shown the first time he sexually abuses Yoonbum he seems to sorta be in a sleepwalking type state where he isn't actually fully awake or aware of his surroundings as evidenced by him calling Yoonbum his mother's name.

and later on after Bum takes his money and goes to a Sauna to get away from his Uncle and later when his Gran tells him he can sleep in his Uncle's Room since he'd be out but then his Uncle returns and savagely beats Yoonbum before commenting that a friend of his in education said that Physical violence doesn't always work as a punishment.

and afterwards he Rapes Yoonbum for the second time do you think he remembered that he had already done it before?

I'm not really sure Wether that makes it worse or not as either A. he did remember Raping him and thus knew that the only reason he took his money for the Sauna was to get away from him due to being traumatised but his Uncle decides to Punish him by Raping him again anyway as a cruel irony.

or B. he didn't know he had abused him before and maybe thought he was just being a Brat by taking his money but Genuinely thought to himself that this was the only way to force Yoonbum to behave.

like I said not really sure what's worse.