Everything would be fine, but little girls don't become liars out of the blue. It looks like Ji Won suffered from the teacher's actions herself... or at least saw them.
So many times in previous episodes, they gave hope that they would close this line between Eun Jae and her ex, even if she already realized this time that it was over and continued to live on. She was already very obsessive, and at the end of the series she was already completely obsessed.
They take such good care of each other..
one of the best episodes of this season, pierced through.
It looks like Ji Won suffered from the teacher's actions herself... or at least saw them.