In Petrarch's Sonnet 90, the theme, as usual, is unrequited love, which he inserts in the parentheses:
(Seldom they shine so now.)
The sestet presents not as a solution but a meditation. The speaker meditates on the nature of love after he has lost his love and after she may have lost her beauty. Whereas her looks are temporal and fleeting, his love (or the wound where it used to be) is permanent (lives on).
I know my first, real heartbreak has never fully healed. Has yours?
Whereas the octet presents his love as mortal beauty, the octet presents her as "divine," godess-like, "angelic":
She did not walk in any mortal way,
But with angelic progress; when she spoke,
Unearthly voices sang in unison.
She seemed divine among the dreary folk
And then, the last two lines:
You say she is not so today? Well, though the bow's unbent, the wound bleeds on.
We have rhetorical question which acknowledges that she may not be as beautiful as she once was. Even so, he says he still feels the wounds from Cupid's unbent bow of love. The heart is still open and bleeding long after it was first shot.