Ok, so he doesn't want to remember anything, that should make everything simple, right? Just when it looked like Na-young was on the verge of giving up on Sang-jin and leaving him well enough alone, letting him have his new wife and herself have Hyun-pil, wouldn't you know it, Hyun-pil has to spill the beans! What a poor liar! Now that Sang-jin's mother knows, it won't be long before the whole world will know,and will never let the poor guy have the peace of mind he seeks. Too bad his own relatives can't be as tactful as his wives.
He has stated he is is happy with his current life, and doesn't want to return to Seoul, because he "gets dizzy" there. Could he be forced to undergo 'deprogramming'? Even though he is currently child-like, he is an adult, and should be able to control his own life. Of course, it's a different country and a work of fiction, and I've seen all sorts of laws and logic fall by the wayside in American TV fiction.