For unrequited love, from Poetry Soup. The rest of the poem may be found here:
http://www.poetrysoup.com/famous/poems/best/francesco_petrarch
from Though She Be Less Severe, He is Still Not Contented and Tranquil at Heart / by Francesco Petrarch (1304–1374)
From time to time less cruelty I trace
In her sweet smile and form divinely fair;
Less clouded doth appear
The heaven of her fine eyes and lovely face.