Honestly, W for Suji. She was literally just a better Jisuwon. Changed herself for him and confessed. Jisuwon at that moment realized that if he accepted it, it would have been a pity acceptence, like Seowlrim accpeting jisuwon if he confessed to her. My headcannon is that suwon realized that he would not want something like that happen to himself, and jisu is just himself. Which is why he decided that he will give up after confessing to Seowlrim. Since we know seowlrim has a shi*** personality and don't have a crush on her, we find it horseshit that he rejected. From his perspective, it is a very thought out rejection.