Responses
I don’t think he knows about that. It looked like they made up a story. I think he’s just upset he has a younger sibling after being an only child for 17 years.
I mean how would y'all feel if your parents told you that one parent ran away for a bit? Running away from responsibilities and life changes of being a new parent? I'd be bratty too.
I only guessing, so I think until Byul gotten older he's being bratty that Hyesung ran away temporarily from Dojin and him when he was a baby.