so i got quite a few comments adressing this topic, so i chose to explain it... i mean, i'm the author anyway

SEUNGYOON'S SEXUALITY

as said in the story, yoon is gay, meaning that he is attracted to men and this doesn't change until the ending of the story, which also explains why he is attracted to taehyun

BUT he is in love with kyungmi/her personality, because she always stayed with him and was there for him, that's why he couldn't fall for taehyun the same way

first he loves her as a friend, but as time goes by it's more in a romantic way, though he takes a while to realize it

so in conclusion you could say he is homosexual an panromantic, since these refer to two different things

i hope this made sense and could clear your questions a little