How to say romantic something brewing in Korean
Korean: 썸[ sseom ]

Meaning
썸 means two people are starting to like each other in a romantic way, but they are not officially dating yet. It is a common slang word for that in-between stage when something is slowly growing. People use it when talking about a new crush or a possible relationship.
Example sentences
나 요즘 같은 반 친구랑 썸 타요.
These days, I have something going on with a classmate.
친구들한테는 아직 썸이라고 말하지 않아.
I haven't told my friends that we're just kind of seeing each other.
회사 동료랑 썸이 생겼어요.
I started a little romance with a coworker.
집에서 엄마가 내 썸 이야기를 물었어요.
At home, my mom asked about my little romance.

