Managed from start to finish; a leap for me!
Like the WIP of before, I think a lot of people tend to forget what Brynjolf is in his core: a thief.
This glorious, impossible man to swoon, is like a wild animal. You can only really appreciate them in their natural habitat, from afar, where you can admire their totality of their person and context.
So I think the reason that Brynjolf is unmarriagleable is that the man is already committed! To the Thieves Guild. You can tell he really worries about the Guild and its members and definitly acts a bit like a big brother to everyone - Delvin would be the cool uncle sorts. I'm fine with not marrying Brynjolf, though ye gods if that were an option I would've SO FAST, with a "Howdy" a day from 'im I can manage.
Remember that when you tame a wolf it loses it's "edge", and by then it's nothing more than another man's dog.