What Is The Most Romantic Song That You Have Ever Listen To?

All I know is, whenever I perform "I Can't Help Falling In Love With You" (Elvis from Blue Hawaii ) every couple in the room gets up to slow dance and most of the men are singing in their lady's ear. Empirical evidence.....

I agree that it is a lovely song with the classical melody of Plaisir d'amour.  Original song is similarly very romantic -
Joan Baez in French and English https://www.youtube.com/watch?v=2tfDf8cYs08
Great tenor with superb video production & translation https://www.youtube.com/watch?v=GcrNF8cxAbI
Great soprano version for men https://www.youtube.com/watch?v=IjBNp07_qok
Great baritone version for women  https://www.youtube.com/watch?v=JQLn86MlaZE 

Male Sextet-King's Singers https://www.youtube.com/watch?v=ZCXCcrXkDxc

From the Movie Spinal Tap, the piano bit supporting a new song named  "Lick my love pump"

Bed of Roses by Rex Benson and Steve Gillette.
https://aboutthesong.com/Blog/BedofRoses
Scroll to the bottom of the page to hear Steve Gillette and Cindy Mangsen sing the song, and some other interesting versions as well, including Kenny Rogers. Speaking of Kenny, Islands in the Stream with Dolly is another good one.

Dylan's "To Make You Feel My Love."

Covered by many, but my favorite by far is Mick McCauley & Winifred Horan's version on their 2005 album "Serenade." Merely sublime.