再美也只是曾经再想也只是过去
[zài mĕi yĕ zhĭ shì céng jīng zài xiăng yĕ zhĭ shì guò qù]
'No matter how beautiful it was, it was only in the past; even if you want it now, it's nothing more than a thing of the past.' This conveys melancholy over lost opportunities where something once cherished may be gone or unreachable now.