If you read the wedding threads, it does seem to be a current ‘thing’, but I honestly don’t get it. It’s not like you have loads of time to sit & chat with each guest. Plus, it’s just rude, it’s as good as saying ‘You meet my requirements, but I don’t trust your judgement’..
I don’t even agree with sending invites without a +1 (if you wish), I think it’s mean to make someone go to a wedding in their own if they have a partner, it’s so ‘We want to celebrate our relationship, but screw yours’. The only exception is maybe if you both have lots of work friends and they come as ‘work groups’.
WWID in your situation? I’d talk to my close cousin. I’d say that I’ll come, but that I’m worried about him. They’ve only been together 18 months and he’s allowing her to stop him inviting someone, he knows and likes, to his wedding, for no particular reason. That doesn’t bode well for a future together. I’d tell him it’s not too late to postpone, or cancel, the wedding.
If I was your DF I’d be relieved I didn’t have to go (weddings are boring) but also a little pissed off on your behalf and I’d feel a bit disappointed in your cousin for being so wet.
Have you met her?