He didn't divorces Dajeong, but Yura. The girl from latest chapter was his HS girlfriend. Author stard he was the jock type of guy, never single, always surrounded by girls and friends.
And they probably do bc Korea is very homogeneous country, even in school standing out is punished and uniformity is praised. I think it it has something to do with confucianism, not only in korea but east asia overall.

i fucking forgot that mc is a divorced man lmao and i forgot the reason why him and probably that dajeong divorced. but anyway bro poor ian, i don't understand why people pick on someone just because they came from a different place/country and just because they have different features. we're all from one planet, we're all the same just different environment and experiences in life. maaan i feel like i'm some wise old man here, i think this is what 2am does to one's brain heh.