My theory: I guess Hee-Do suffers from a K-drama level amnesia, that made her forget her memories from childhood…
in a previous episode, when Hee Do chat with her mom, in present days, her mom told her that she meet Yi Jin a month ago and Hee Do seems uncomfortable hearing about him, like she dislike about it, so ...
i want to believe that the last scene/last ep, when she call his name she made a heart with her hands for him :) (and that's my romance imagination :)))
poor you!