My Dad's Friend, Whom I Thought Was a Gentleman

Feeling lonely after breaking up with her boyfriend, Lee Seo suddenly develops a sexual attraction to Kwon Yitae, her father's long-time friend. But one late night, Lee Seo completely succumbs to the subtle seduction of Kwon Yitae, who is staying over at their house. The man she has always known as kind and gentlemanly finally begins to reveal the feelings he's kept hidden all this time... The secret side of her father's friend, who she thought was nothing but a gentleman. And so, Lee Seo begins to see her father's friend as a man. This marks the beginning of a relationship that should never have begun between the two of them, and there's no turning back.

(Source: Lezhin Entertainment, translated)