Its probably
'you can't change the past'
'that phone call was always meant to happen'
'YeaonHo caused Jaeha's death'
etc
sad :(
If I remember correctly, at first Yeaon-Ho didn't know why Jae-ha died.
Now it's 1000 times worse to know that he's one who cause him die twice.
I don't really know where this manga is going so I don't know if something will happen to change this, but it's not just twice.
Well it is. But it's not...
You could argue that Jaeha dies both once (cus there's only one Jaeha!) and also an infinite number of times throughout all the different timelines. (since the younger Yeaonho is also gonna get on with his life, move back, find a weird phone and cause Jaeha's death)
Timey Whimey stuff ':)
Pardon me, sensei.. If you make Yeaon-Ho can't save Jae-ha then what's the point of making him connect to the past 10 years ago. That's like giving Yeaon-Ho hope just to kill him who's already like a dead man walking!┗( T﹏T )┛