It’s quite subjective. If a good looking athlete or artist dated a woman who he knew when she was 16 but he was an adult, there wouldn’t be much outcry. But if a regular looking teacher dated a student he knew when she was 16, it would definitely raise more eyebrows.
I mean, I get your point but are we sure they were actually dating when she was of that age? I know there were rumours they had been dating for a year before their apparent split. fair enough, but were they really dating when she was 16? I am just asking. I seriously don´t know. In that case, since the age of consent in Korea is 20 years old, that would seriously be illegal and controversial unless they were like holding hands for 4 years which with all due respect to GD, I doubt they would do? (or maybe they would but... )
You would be surprised that while a lot of countries forbid their teachers to date their students aka meaning they would be fired on the spot, a lot of countries do allow that as long as the student is older than the age of consent. For example, here the age of consent is 15. A friend of mine had a classmate who had a child with her high school teacher, she was 18 and was a stepmother to his children as well as being a mum at 18. Of course there were odd looks and moral questions, but the teacher did not lose his job. Technically he did nothing illegal according to general law or school rules.