Idiom

쿨하다

kulhada

To be 'cool' about something - not clingy or overly emotional about it

감정에 연연하지 않고 시원시원하게 행동한다는 뜻

헤어졌는데도 쿨하게 잘 지내더라.

Even after breaking up, they were being really cool about it.