当时轻别意中人山长水远知何处
[dāng shí qīng bié yì zhōng rén shān zhăng shuĭ yuăn zhī hé chŭ]
It means 'Back then I parted easily from someone in mind, but now with distant mountains and long rivers, who knows where they are?' This reflects nostalgia and sadness over parting ways unexpectedly with a loved one and the regret felt afterwards.