The trope is specifically about when the writer honestly believes their story's ending is happy, but the readers don't, generally because the story did not convince the readers that the ending would actually be a good outcome. Setting aside the fact that the trope only pertains to a reaction that the writer wasn't expecting, the way you're describing your ending doesn't sound particularly unhappy, it just sounds like an ambiguous situation, if that. And this might just be me, but having a plot thread that is allegedly shoehorned (meaning clumsily forced into the story and possibly distracting) and also the primary focus of the ending sounds like a bigger problem than an ending that doesn't seem to be exhibiting the problem you're describing.
"Jack, you have debauched my sloth."
Crystal Glacia is right. Esoteric Happy Ending is about how (some of) the audience reacts to your ending, so you can't really write one on purpose. I believe that what you're looking for is Bittersweet Ending.
Edited by Kickisund on Sep 9th 2018 at 8:52:43 PM
Is a Esoteric Happy Endining a good or a bad thing to have in your story? I have a esoteric happy ending for one of my characters in a story that runs on Maybe Magic, Maybe Mundane .
This character marries in the end of the story, but that is not the only happy ending for him. He can possibly get an Esoteric Happy Ending as well . This story has an 50/50 chance that he is a human with a soul or a monster without a soul. And a marriage with true love between a monster & a human gives the monster a soul...
I half shoe-horned in the love-story into the story, half was "forced" to it because of the inspiration for the story. (Medieval ballads, fairy-tales & such.)
I reject your reality and substitute my own!!!