EVERYONE SAY THANK TO @conscience-grim FOR SHARING THIS ABSOLUTELY WONDERFUL INFORMATION WITH US
Montersor very likely died and lived around the same time as Lenore, late 1800’s to early 1900’s, and during this time. Pretty boy was slang for a gay prostitute in southern America and north UK.
Montresor, is literally calling Prospero a gay whore in the scene.
This also makes the head canon of Annabel calling Lenore “pretty boy” SOOOOOOO much funnier, because Lenore likely knows what it means and Annabel doesn’t because she is aggressively, southern English, so she would use it in the same way that we use it today literally just calling someone a pretty boy. LENORE HOWEVER.
Annabel, lovingly stroking her fingers through Lenore‘s hair while she lays her head in her lap: Oh, look at my pretty boy <3
Lenore, flustered, abruptly raising her head: EXCUSE ME- HEY! IM- I AM NOT-…..
Annabel, oblivious, thinking Lenore is just being bashful: Oh! But are, pet! You are so pretty and your mine, therefore, you’re my pretty boy!
Lenore, fully thinking Annabel’s calling her her bitch: 
I want everyone to imagine Annabel saying this, while they are still alive at a party or something. The whole room stops and turns to see the most fashionable power couple that high society has seen in decades. Everyone is falling over this new, mysterious, dashing rogue like character, Leo vadernacht, nephew, and now air of the entire Vandernacht railway empire, newly engaged to the most, sought after bachelorette in the entirety of English and American high society, the most Lady like and proper Annabel Lee Whitlock. And she proceeds to turn to her fiancé and call him her gay whore lovingly. IMAGINE THE REACTION
And to add onto this, Montersor isn’t a cowboy. He’s heavily implied to be a horse breaker, which is basically a priest, who also doubles as a horse tamer, and only in the UK was this term known as slang, for once again, a gay prostitute.
So I want you to imagine Monty casuallymentioning he was a horse breaker while he was alive and Annabel FULLY TURING TO HIM LIKE
SHE MUST BE SOOO CONFUSED WHY ADA’S STILL DATING HIM
Annabel: I went through so much trouble to make sure no one figured out that me and Lenore were gay, just for this bitch to come out and fully admit he’s a gay whore with little to no consequence.