The illness of the heart is not a custom of the city of beauty; otherwise, even the innocent beloved would know how to cure this pain.

This profound couplet explores the unique agony of heartbreak. The poet suggests that the pain in the heart is so deep and unusual that it doesn't follow the 'rules' or 'customs' of the beautiful world. If it did, the innocent beloved would surely know the cure. It speaks to a pain that transcends mere physical remedies—a wound only time, or perhaps fate, can heal.