忧伤不解你已走
[yōu shāng bù jiĕ nĭ yĭ zŏu]
The online name conveys an unfathomable sense of sorrow and regret after someone's departure. 'Don't understand you have left' suggests that there may have been some unresolved matters between both sides before this person left, leaving the user feeling sad but helpless about the past.