曾经深爱过你是你不懂珍惜
[céng jīng shēn ài guò nĭ shì nĭ bù dŏng zhēn xī]
The phrase means 'I once loved you deeply, but you did not cherish.' It expresses past love and regret. It is a statement often used after the relationship has ended, lamenting lost love and misunderstandings.