
He isn’t getting divorced, rather, the woman he was dating ended it so she could spend more time with her daughter. A strange reason, in my opinion , to break up with your lover, but there it is. So the Director was only dating someone, not married, and then got dumped, but in a friendly, loving way. Hope that clears some things up :)

“Really quick for a straight guy” - Imo that’s why you shouldn’t even be using these fictional stories made by women as proof or evidence that a story doesn’t seem “realistic” enough to you. None of these stories are realistic, they’re fantasies written by primarily female writers for female readers.
That said, in real life, it is not uncommon for people to discover their sexuality until later in life after meeting the right person, or just discovering they’re open to experimenting.
Just some flaws (or I didn't catch-up)
1. At what point does Director Kang develops his feelings for Yiyoung? 'Cause all I see is that he is too formal to Yiyoung and the way his body language is too awfully confusing to me and suddenly, poop! he was already falling for Yiyoung.
2. This is also related to no. 1. Director Kang is straight and is on the process of divorce(?) then suddenly have a one-night stand with a guy then he just flick it out as if it's just for experience then suddenly yet slowly become interested to a guy. Well, that is really quick for a straight guy (sorry, I've just read a good yaoi about a straight guy-gay relationship so I'm unconsciously comparing them) or Director Kang is a different kind of guy as what the author wants to portray him.