Responses
He had always loved or atleast was interested in MC since highschool, despite it being unsaid. Even until their reunion, there's always the lingering feeling of yearning left from him. He's also always been gentle to him since the beginning, but because of a misunderstanding, he felt betrayed and that's how their relationship ended.
So after their first mingle, he realized that it wasn't so bad and his yearning for Ihyeon grew stronger and stronger. Which is where we are right now.
If you want to learn more: https://www.mangago.me/home/mangatopic/23591185/
Why ML suddenly acting good to MC ? (⊙_◎)