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

“At This Moment” Billy Vera and the Beaters. Also covered by Michael Bublé. “If you stay I would gsubtract 20 years of my life.” Hauntingly beautiful in every way.

Some of the choices here are very surprising.

"Make It With You"
Bread
(now that the Nine Inch Nails Nineties are over....)
https://youtu.be/s0KXV0gB0dw

"Maybe I'm Amazed" (already mentioned) is an incredible love song.

I'm amazed that PM is able to make it through it.

I also like "Sara Smile".

Not certain if the OP's query is meant to include love songs, which can differ from romantic songs.

DeKay

Hats off to Mickeyb for Grant Lee Buffalo and Honey Don’t Think….unique vocal style.
Can’t believe I’m saying this but, 
ELO - Telephone Line
stops me every time.
Unrequited love doesn’t really qualify as romantic…or does it?
Elvis Costello - She is my GFs choice