The couple used to have disputes in the past regarding giving less time to their kid especially the mother due to job outside the country(as the father was present at least on graduation) and the ML as a kid might have heard them talk as a kid where he might have heard something disturbing for a kid ( like, "I didn't even wanted him ") ; and thus came the bad memory ( if you know from which c-drama this theory is inspired then don't hesitate you're right) If you remember episode 2 or 3's breakfast scene of ML family he said " you usually don't stay here " or something like that. Which though might have looked to his mom as him having problem from her or him not being happy of her staying but we know as the viewer that ML was expressing bitterness regarding how she's not usually with the family at home. As for the divorce message, I think ML mom and dad might have made some kind of agreement regarding , that they'll remain married until ML becomes adult or settles down , and the reason for that being----- Either her career or ML father may have seen ML mom and vice minister talking friendly and might have misunderstood and thus under the pretext of giving reason that for her career they'll divorce but only after ML becomes ….. Finally that coughing up while drinking water on affair being mentioned, either the ML father accused the mother of affair(which I hardly believe) and ML listened ( became bad memory) and then came divorce talks with agreement. OR this being K-drama, ML father might have thought" damn she looks happy with that guy let's make a false story of me cheating on her and in that pretext divorce her for "her" happiness. and then came agreement of divorce. The father might have forgot about that but after seeing those two together, he might have thought, " F**k, S**t, B**ch , thought I had a chance, let's follow the agreement ." and thus "AFFAIR" word became something for her to cough up her water. Oh, and bad memory was not part of the sacrifice reason , bad memory might have come through theory 1 in the sacrifice case.
If you remember episode 2 or 3's breakfast scene of ML family he said " you usually don't stay here " or something like that. Which though might have looked to his mom as him having problem from her or him not being happy of her staying but we know as the viewer that ML was expressing bitterness regarding how she's not usually with the family at home.
As for the divorce message, I think ML mom and dad might have made some kind of agreement regarding , that they'll remain married until ML becomes adult or settles down , and the reason for that being-----
Either her career or ML father may have seen ML mom and vice minister talking friendly and might have misunderstood and thus under the pretext of giving reason that for her career they'll divorce but only after ML becomes …..
Finally that coughing up while drinking water on affair being mentioned, either the ML father accused the mother of affair(which I hardly believe) and ML listened ( became bad memory) and then came divorce talks with agreement. OR this being K-drama, ML father might have thought" damn she looks happy with that guy let's make a false story of me cheating on her and in that pretext divorce her for "her" happiness. and then came agreement of divorce. The father might have forgot about that but after seeing those two together, he might have thought, " F**k, S**t, B**ch , thought I had a chance, let's follow the agreement ." and thus "AFFAIR" word became something for her to cough up her water. Oh, and bad memory was not part of the sacrifice reason , bad memory might have come through theory 1 in the sacrifice case.