Based on the recent chapter, 57. ML didn't actually had an amnesia due to the car accident with MC. "He thought you(jiyoung/mc) died." Either its his older brother who lied or his father.
In earlier chapters mentioned ML had a car accident, im guessing they meant his first car accident with MC but seeing how he didn't get his amnesia in this recent chap(not sure but it seems so).
Maybe the ML got into another car "accident" like as in on purpose, su¡c¡de yk? based on his character he seems like the type to do that if the MC is de3d.
As in the type to go, "If you die, then i die too" or "If aren't alive what's the point of living any longer?"