你非我良人怎知我心痛
[nĭ fēi wŏ liáng rén zĕn zhī wŏ xīn tòng]
The sentence literally says “if you’re not my beloved, how do you know my pain?”, meaning the one who really understands the depth of one's feelings is none other than the one who has a close relationship, often romantically, with oneself. The expression conveys an unfulfilled longing mixed with loneliness that only true love can fathom.