Stop defining people by their sexuality it dosent matter if Sangwoo say he is “straight” he still loved Bum and had a realationship. People can be straight, gay, lesbian etc and still have sex or love a person that isnt the vender they usesally like.. you can love whoever you want and sexuality is just a stupid label we put on our self to Either hide our true feelings or to tell others our sexual preference.
No wait, Seungho doesn't suffer from BPD, Bum has BPD. Sangwoo is extremely violent because it's his response to trauma and to all the abuse he witnessed and experienced as a child. But you are right saying the author confirmed it. It's 100% canon Sangwoo loved Bum. What people don't understand it's that KS shows the complexity of human nature, abusers are able to love too. The world is not black and white and sexuality and feelings are complex and nuanced.
I think they both suffer?? Like it seems as they both presentate borderline.
Fear of abandonment. - Sangwoo and Bum
Unstable relationships. - I’m a little unsure with this one
Unclear or shifting self-image. - Bum
Impulsive, self-destructive behaviors. - Sangwoo
Self-harm. - Bum
Extreme emotional swings. - Sangwoo
Chronic feelings of emptiness. - Sangwoo
Explosive anger. - Sangwoo
Feeling suspicious or out of touch with reality. - Sangwoo
Correct me if I’m wrong but they both have symptoms for it.

im ok with everything about this story expect how in the end Sangwoo called for bum
so stupid and ruin character personality in the end
Sangwoo attracted to women, story mentioned many time he is not gay or love guys, he just cant love anyone but in the end seems author try satisfy some weirdo shippers of them
its just so out of character
i seriously loved season 1 and 2 of this webtoon, author just changed her pov so much in season 3 to satisfy fans of this series