There has been Bi characters in KDrama history, and it's been explored more in the lesser-known webdramas and family dramas that are more complex with more storylines attached. Though it's not outright said, it's implied in one way or another.
In the case of this drama, I think it's a one-sided type of love. It would be surprising if they go into depth with sexuality at this point. At 18 and and Cheese in the Trap are the only ones I've watched with male gay characters but they were brought in and thrown aside.
In the new age of dramas such as Itaewon Class, and even Romance Is a Bonus Book- other parts of the LBTQIA+ spectrum I think are starting to become more mainstream due to social media from the West... but only time will tell. Heck, in Revenge Note 2 there was a character who was considered more masculine and multiple characters mistake her for a boy.