Is All Love Sweet?

Today is the anniversary of the birth of Barack Obama and Louis Armstrong (interesting coincidence), but also Percy Shelley.

Shelley wrote

All love is sweet,
Given or returned.
Common as light is love,
And its familiar voice wearies not ever.
They who inspire is most are fortunate,
As I am now: but those who feel it most
Are happier still.

The quotation immediately brings to mind the line from Shadows and Fog,

"There's only one kind of love that lasts - unrequited love. It stays with you for ever."

So, Shelley the romantic or Allen the cynic, who is right? Is all love sweet?