曾经的海誓山盟以后的空城旧梦
[céng jīng de hăi shì shān méng yĭ hòu de kōng chéng jiù mèng]
Literal meaning is “Once vows are just the old dreams in the abandoned town afterwards”. This suggests broken promises in the past, and it often indicates a failed romantic relationship, reflecting melancholy, sorrow, and disappointment after an experience filled with hope turned into nothing but memories in the end.