当爱你成为习惯当思念变成习惯
[dāng ài nĭ chéng wéi xí guàn dāng sī niàn biàn chéng xí guàn]
It means that loving someone and missing them have gradually become a habit or routine in the speaker's life. This suggests that love is deeply ingrained into everyday activities as well as when apart from each other.