I get that Jang Ki-young has insane screen presence and the chemistry looks intense — he’s great at that.But…
Honestly, she's actually single, so if she plays his game, it's because she knows she can. She also made up the biggest lie by saying she's a mother and married, so if in any way the boss's attitudes seem a bit too much to her she can always resign, since she shouldn't be working there anyway. I'm not saying he's being right to her, absolutely not, but since she's the first to let him doing certain stuff, he kind of continues. Anyway, I haven't seen any attitude so scandalous of him as you say. Even the other mothers on many occasions stayed late working in the office. in conclusion they are the two protagonists so it is clear that at a social level fiction requires that there are certain occasions in which to show the two protagonists attacked etc...
I really don't understand