My guess, triggered by comments (EDIT: augh! It's Stender's exactly! Ah well -- here is some more explanation to support his guess -- he gets the credit):
John is
the moon
and Marsha is
the sea
Dear John,
My actions fail me through the years
So now I'll speak through windswept tears.
"windswept tears" -- wind on sea waters creates spray
I'll never get your wandering ways;
The moon constantly revolves around the earth, where the sea is bound. [OP:It wobbles, too]
Remote attention fickly sways.
You leave me swirling, dazed, and lost in gloom.
The moon creates tides from afar.
To stalk is hardly my intent, no.
I follow you, so that you'll know
There's life inside me and I feel
The sea holds plentiful sea life. [OP:The ocean "follows" the moon]
The bond between you two is real.
Remember how we danced that night in June?
https://oceanservice.noaa.gov/news/high-tide-bulletin/summer-2017/ noted higher-than-normal tides [OP:This was a nod to the theory that life arose from tidal pools... and "June" simply ≃ a rhyme with "Gloom"
You're cold, you're distant, tantalizing.
Metaphorical aspects given to the moon.
I don't think that you'd despise me.
I can see it, no use lying:
Your face would never truly rise
Against my salty eyes—you know it's true.
The sea is salt water. [OP: the moon has a face that rises]
I'll not give up; yes, I have found
That men like you will come around.
I'll channel deep, I'll find the grace
"channel" is a cue to the sea -- channels being waterways, like the English Channel [OP: men, like the "man in the moon"]
I'll give you what you need—your space—
The moon is in space.
And love you from my depths when you are blue.
The sea has depths, and folks are familiar with "blue moons".
I love you.
-Marsha