Dylan's "Isis" is a good lovesong -- and very well written
Leonard Cohen's "No Cure for Love"
Richard Thompson's "Dimming of the Day"
"Ca' the Yowes Frae the Knowes":

"While water ripples to the sea
While the sun blinks in the heavens sae high
'Til clay cold death shall blind my ee
Ye s'all be my dearie"

"When You and I Were Young, Maggie," and "The Dutchman," as stated above.

Great traditional songs of unrequited love are too numerous to list, but include "Loving Hannah" and "Fond Affection."

In the shameless self-promotion department I submit "Wallflower Waltz,"
"An Early Valentine" and "I am Your Winter Lover" which can be heard on my first recording and "Westron Wind," which will be heard on the next one (I used the famous quatrain as a chorus and wrote six verses for it and a new tune).

Dave Webber's "Bonnet and Shawl" is a lovely and hopeful lovesong.

As for love itself, I can do love of pets and love of friends and even a bit of love of family, but romantic partnership eludes me thus far.