Well he is pissed!! Who wouldn't be if your lover take you on holiday just to break up with you? He wants to hurt him as much as jaeha did.
if your loved one hurts you a great deal you either accept this sick relationship as is OR you stop the relationship because it hurts too much.
you never try to get any sort of 'revenge' and hurt them back because this ping-pong game of you-hurt-me-I-hurt-you-back is not love anymore and totally stinks!!!
seriously, right now I cannot think of any proper excuse for this behaviour towards a person he absolutely admired and cherished.
Please stop calling this degrading mess 'character development'... he's wrecking them both with these actions, the boy is unwell!
Fuck you Makio. Fuck you