What is the name of this drama?

From what I can remember
This lady I think takes the identity of some lady and ends up teaching in a school after the lady dies in a bus accident. I think she falls in love with a guy who has a “learning disability” but he becomes smart after surgery. I think the surgery helps for long.

Can’t remember if it is a K/J/C/T drama

I have no idea… do you remember something else? Like… why did the first lady take the identity of the other lady? Or a name of a character? Or a song? And school? High school, I assume? Old drama?

The more you remember, the easier it might be to identify the drama ^^