This is so well-written and you've created such a fascinating world. I did love the initial revelation that 'the most common soulmate mark in the world consists of the words “Sorry, what did you just say?”' Something I'd never considered before but it makes such sense ^^

And I did so admire how the rules of your world both transformed and explained the characters' actions - as John is definitely her soulmate, Mary is confident enough to tell him about her past; Sherlock believes John can never be his, so there is a good reason for him staying away after faking his death.

There’s more trouble coming, of course (there always is), but with the three of them facing it as one, he knows there’s nothing they can’t weather. Perhaps not a 'happy ever after' but I'm glad they get a hopeful ending.