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.
i really read this 5 years ago without batting an eye huh....