1. What does it mean?
썸붕 combines 썸, the ambiguous flirting stage, with 붕괴, collapse. It describes that connection fizzling out or ending before the two people clearly become a couple.
Also written or said as sseombung
2. The nuance
It is different from breaking up an established relationship. The cause might be incompatible expectations, timing, or fading interest; the word does not assign fault by itself.
3. Examples
“몇 번 만나다가 서로 일정이 안 맞아서 썸붕이 났어.”
We met a few times, but our schedules didn't line up and the connection fizzled.
“썸붕 후에 상대를 탓하기보다 내 마음부터 정리했어.”
After things fizzled out, I focused on sorting out my feelings instead of blaming the other person.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.