The first time I read this I didn't look as deeply into it... but rereading, i feel that it's very clear Woojin liked Gayoung long before her actual confession. He just repressed his feelings.
The way woojin was never interested in anyone else BUT gayoung??? Even with eugene he turned cold on her and basically said "do whatever you want" making it obvious that he doesn't really have deep feelings for her even though he THOUGHT he did. The only one he'd ever fight for is Gayoung. It was clear he had a pessimistic view on love and couples throughout the story, like whenever he'd think about them or look at them, he seemed kind of gloomy. And this most likely stemmed because of his situation as a kid with his parents fighting so much, his father cheating, his parent's divorce, etc... So he blocked out whatever feelings he felt for gayoung along the way: not wanting to deal with that, and basically being scared of relationships and commitment. This becomes really clear after Gayoung confesses and Woojin says he's scared, and it cuts to his flashbacks of his parent's relationship and essentially how he thinks that "love cant last forever".
The first time I read this I didn't look as deeply into it... but rereading, i feel that it's very clear Woojin liked Gayoung long before her actual confession. He just repressed his feelings.
The way woojin was never interested in anyone else BUT gayoung??? Even with eugene he turned cold on her and basically said "do whatever you want" making it obvious that he doesn't really have deep feelings for her even though he THOUGHT he did. The only one he'd ever fight for is Gayoung. It was clear he had a pessimistic view on love and couples throughout the story, like whenever he'd think about them or look at them, he seemed kind of gloomy. And this most likely stemmed because of his situation as a kid with his parents fighting so much, his father cheating, his parent's divorce, etc... So he blocked out whatever feelings he felt for gayoung along the way: not wanting to deal with that, and basically being scared of relationships and commitment. This becomes really clear after Gayoung confesses and Woojin says he's scared, and it cuts to his flashbacks of his parent's relationship and essentially how he thinks that "love cant last forever".