Responses
I think towards the end Sangwoo was going insane and was paranoid. I think he thought Bum was going to poison him like his mom was.
I don't think he hated Bum PER SAY.. I think he just thought he would be betrayed again and want to kill Bum to prevent that from happening. Although we know Bum was just tryna be slick with the rings but hmph...
Sangwoo might still hate and wanted to kill Bum till the very last of his breath for he thinks that Bum betrayed him. That's one of the reason to consider why he keep repeating Bum's name on his deathbed.