Hol Horse had used magic to turn into a pony. Oingo had used Khnum to turn into a changeling. Boingo was the only other one of the group left who was still in his original form.
 
But Boingo wasn’t the one who was in a relationship with another species.
 
 
“Ditzy did say that interspecism was becoming more common in Equestria. I think I even recalled her saying something about her niece dating a dragon. Or was it a griffon?” He wondered aloud as he glazed over the books on the high shelves.
 
Even before they had started dating, she was upfront and honest with the fact that she was a pegasus. He didn’t really mind, as she was (at least temporarily) the same species as he was. He’d been through quite some bizarre things in his life, and he simply added ‘dating a pony’ to the list of good bizarre occurrences.
 
 
“But they’re all magical creatures. They all have claws, or beaks. Feathers, fur, or hooves. Hell, even Umbrella Beach* morphed into a pony.” He sighed, opening a book titled “Sapient Sapiens: What We Know About Humans”
 
“There haven’t been enough visits between the dimensions.” He quickly flipped through it, putting it back as he had seen most of the information before in biology books.
 
“What other human could relate to falling in love with a mare?”  
.  
.  
.  
“There, there, Jean. It’s gonna be alright. You can tell that little pony you love her.”  
“Easy for you to say. You’re a stallion, part of your own ‘little pony’s’ original dimension.”  
“Not exactly..”  

 
Minor spoilers for the Polnaderp fanfic~ It’s still a bit of a work in progress.  
*Umbrella Beach is Derpy’s Stand.