I really really think that what had happened was that both Yeo Hwa-jung and Jang Young-guk had fallen in love with Yu Cho-hui. And then she left. So heartbroken and lost Hwa-jung and Young-guk decided to lean on their friendship and get married. I think Young-guk may have eventually developed feelings for Hwa-jung, but I don't think she was ever able to reciprocate and hence she asked him for a divorce. It also explains why shes fine with Young-guk dating literally anyone but Cho-hui. She's still carrying a torch for Cho-hui.
And if you draw parallels between the love triangle of Du-shik, Hye-jin and Director Ji, then Young-guk is Director Ji, being straightforward about his affection, Hwa-jung is Du-shik, insisting to come along for meals, but also pushing their affection away, and Cho-hui is Hye-jin, somewhat oblivious to Young-guk's affection and subtly longing for Hwa-jung's.
Idk what tvn's stance on LGBT+ relationships and depictions are but as a Netflix show maybe there is more leeway? There was a canonically gay character in Vincenzo (and a whole episode dedicated to a fake romance for him). Idk but the writing, direction and parallels are there.
Hwa-jung even saved Cho-hui from the kidnapper, just like Du-shik saved Hye-jin. Like... When its all laid out like this, its not nothing.
