There's a word missing in the 3rd verse, last line, it's "lloran por el bien que adoran".

Here it is

I sell black eyes.
Who wants to buy them from me?
I sell them for being wizards
Because they have paid (rewarded) me badly.

I'd love you more
I love you more
And I spend all the nights (lit. "the nights, I pass it")
Yearning for your love!

Whenever I have pain
I go to the seaside
To ask the waves
If they have seen my love pass by.

The flowers of my garden
Fade in the sun
And the eyes of my black (one, lady...)
Cry for the good* they adore.

Treacherous black eyes,
Why do you watch me thus?
So glad for others
And so sad for me!

What do you gain for not loving me
And I for not loving you
If (when) I am dying to see you
And you do/can not live without me?

* "good" in this case means "precious one" "love".

In Spanish, the verb "querer" which literally means "to want" usually means "to love" in this case; "amar" only means "to love" but is mainly used in literature/poetry/songs.

The translation to the additional verse Q mentioned is

And the waves answer me
That they saw her* indeed
With a little bunch of flowers
And throwing flowers to the sea.

* "lo" is literally in masculine because the question was about "my love", a masculine word in Sp.