Responses

Spoileer.
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I think sangwoo also jealous when bum accidently sitting on his laps friend.
His expression really change on there.
So i think sangwoo also want to punish him

Well Sangwoo has been emotionally fucking with Bum since the begining, the physical abuse was just more prominent. Bum typically reponds to upsetting things with sadness. Would be interesting to see him angry.
A thought about what's coming next. There are no real spoilers but if you're delicate about spoilers don't read it~.
I think the thing sangwoo was saying about doing something for someone and making him nervous started in Ch 17.
I think he plans to make Mak e bum hate the girl with his actions so bum kills the girl. Maybe sangwoo is expecting bum to understand him more or just to bind him to himself...Well just a thought...Or sangwoo just got tired of absuing him physically and changed to emotional fucking abuse uhwaaaaaah ╥﹏╥