I am trying to find the song Ricky sings at the end of "Second Honeymoon" episode (on the ship):

"My love is true, amor tierno, I promise you amor eterno"

Any help?

I think it is "Cielito Lindo"

No, it's not Cielito Lindo.

This is the script of the "Second Honeymoon":
https://www.springfieldspringfield.co.uk/view_episode_scripts.php?tv-show=i-love-lucy-1951&episode=s05e14

Scroll down to the end of the episode.

"What'll we do, honey? Try to pull me out of here.
Try to pull you out? Is your arm stuck right there? Oh, oh, wait a minute, everybody get together! (straining) (Lucy screaming) My love is true, amor tierno I promise you amor eterno So cling to me, dear, and say You'll never let me go Because I love you so, querida mia.
Oh, that was lovely, sweetheart.
Thank you.
We finally got to be alone together, didn't we, dear? Yes, baby."