相思入骨君可知
[xiāng sī rù gú jūn kĕ zhī]
A poetic expression of deep longing, 'Xiangsi' translates to longing for someone absent, and 'RuGu' means bone-deep or intensely. So this roughly translates as 'You don't know how much I miss you'. It conveys a sentiment of love and unrequited feelings.