既不回头何必不忘既然无缘何须誓言
[jì bù huí tóu hé bì bù wàng jì rán wú yuán hé xū shì yán]
'No need to look back and no need to forget; if there was no destiny together, then why make promises?' This expresses feelings of regret and resignation about a past relationship that didn't last.