But it's irrelevant because it has no bearing on your situation.
I'm in my 50s. About 2 years after I separated from my husband, I was invited to a wedding alone. I was a bit surprised because, stupidly, I'd never even realised it was a thing! 😄 I wasn't going to know anyone else there either. I briefly considered not going but then got over myself because she'd invited me and she wanted me there so I went.
But, when I thought about it, it made perfect sense. Why would they invite and pay for someone that I might not even have been seeing by the time the wedding came around?
As for +1 invites, I wouldn't expect anyone to invite or pay for someone who hadn't even been named!
As for other partnerships, I might invite my best friend's partner of a few months but not the bloke a colleague had been seeing for a few months, no.
It also wouldn't make any difference if they were married. I've got a friend whose been with her partner for 33 years but never married. Of course I'd invite him along.
So established relationships but not someone who was only in the 'seeing' category.