我以为分手可以很开心
[wŏ yĭ wéi fēn shŏu kĕ yĭ hĕn kāi xīn]
'I thought breaking up would make me happy.' Conveys a reflection or realization that while expected to feel relief or joy, the outcome of separating (from a romantic relationship) did not meet those expectations and instead resulted in different or unexpected feelings.