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

Kiss "Lick it Up".

The first time ever I saw your face. Roberta Flack
Cherish.  The Association 
When I Fall in Love  The Lettermen
The Way You Look Tonight. The Lettermen

tl;dr

Somebody (Depeche Mode)

(You’re the only thing) can make me cry - Concrete Blonde https://youtu.be/TA_q0Ahl9XY
Barebones acoustic, it’s simple, genuine, and heartfelt.

If you want a classic that’s a little unconventional, listen to Jimmy Durante sing “As time goes by.” He’s proof that a great singer doesn’t necessarily fit a stereotype. https://youtu.be/duMUG6XwwQ0

Sinatra’s The Way You Look Tonight is another ageless classic and an obvious choice: https://youtu.be/YFham2Xu6nA

Erev Shel Shoshanim - An evening of Roses  Hundreds of recordings
My favorites include https://www.youtube.com/watch?v=Jr8zzS-Gjp4  Malka & Joso
The Parvarim  https://www.youtube.com/watch?v=VEpNy0_EjHU (right two are Simon & Garfunkel look & sound alikes who made a hebrew version of their songs looking just like them). 
Or how about this youth zoom choir Newark Academy
 https://www.youtube.com/watch?v=HNpnH59J6-g