Since the author said that the ending is up to us so I'm gonna tell my ending:
From what I understood, Jae ha definitely died and Yeon Ho died in the crash. The extra chap looks like its in the "after life". They both died and met again in the "after life" cause Yeon Ho said that his parents might reconcile and he wasnt sad saying that in the extra chap.
Since the author said that the ending is up to us so I'm gonna tell my ending:
From what I understood, Jae ha definitely died and Yeon Ho died in the crash. The extra chap looks like its in the "after life". They both died and met again in the "after life" cause Yeon Ho said that his parents might reconcile and he wasnt sad saying that in the extra chap.
So Yeah (⌒▽⌒) That's my ending