im confused, does yoontae know that his first love is jeongseo? and does jeongseo know???

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In the novel, Yoontae knows. Jeongseo figures it out after Yoontae tells him how he met his first love and Jeongseo remembers it. So ch 16 of the manhwa. He doesn't say anything because he thinks he doesn't like Yoontae in a romantic way. (Yet.)