Responses
asknf koogi has actually confirmed to fans at one of those group thingies that sangwoo in fact did fall for bum! i also think that's what she was trying to show with having sangwoo call out bums name in his last moments, instead of his mothers (which someone commented about below)
Sangwoo is heterosexual but it doesn’t mean he can’t fall in love with Bum. I have a friend who is a heterosexual Woman but is dating a lesbian right now. She still identifies as heterosexual. So yeah, Sangwoo could have fallen in love with Bum :)
I still don't think sangwoo ever loved bum in the romantic way but felt a bond for him/need to protect him. The author even states that he is heterosexual and perceives bum as a substitute of his mother (not past tense). I do think he cared for him in the way he most could as his mental insanity could by seeing his deranged dead mother in him but not romantically. I wish the author had just given a straight yes or no answer though since the ending was obviously made to be open ended still.