I'm part of a triad, but people only ever invite 2/3 of us to their weddings

This summer our girlfriend moved in with us. We were last minute invited to the wedding of a girl my husband and I have known for 20 years, and when I enquired about a third seat I was told no. My husband still attended while I refused to. But I eventually just put it down to the fact that she didn't have a lot of time to prepare, we were last minute additions as it was, even "she doesn't get it." I'm not usually bothered by people not understanding because almost everyone I know DOES. So my cousin got engaged and I reached out to him once we learned the wedding is across the country, eight months from now. I explained the situation and was floored when I got the response that they "weren't giving +1's", because she is not inherently less important than my husband. I held back a dozen sarcastic, petty responses - I won't clog up the ask with those - and I think I'll pin our refusal on financial reasons, but I still wish I had better coping skills for this, I guess.

I’m confused - if your cousin isn’t giving +1s, does that mean your husband isn’t invited either? Or that your husband and you were explicitly invited, and neither of you gets a +1, and the assumption is that even single people were asked not to bring anyone not explicitly invited?

The thing about weddings is that they tend to make people go bonkerspants. You don’t know if your cousin’s wife has an Aunt Margarine who will lose her mind if she sees a hint of anything Untraditional, and that they’re worn down and currently unable to pick that fight with her. You don’t know if their budget is super strained to the point that they really just can’t afford any guests besides the people they specifically invited.

I personally wouldn’t pick this fight, or take this too personally. People’s choices around their weddings are usually about them, and the whirlwind of family drama and expectations and nonsense that they’re caught up in, and very rarely a statement on anyone else’s lives. Polyamory is not very well understood by the general populace, and people who are emotionally and financially stretched thin don’t have the ability to parse through the deeply held identities and feelings behind every guest’s extra request.

Your cousin is very likely not intending to say that your girlfriend is “less important” than your husband - he’s trying to set personal and financial boundaries around his own wedding, and in such an emotionally charged situation, it’s easiest to hold to common, if arbitrary, standards around +1s and invitations. I understand that it’s really hurtful to get that message, but not all “messages received” are “messages sent,” so try to give your cousin the benefit of the doubt. It’s okay to decline the invitation, but it’s also okay to talk to your girlfriend about whether she’d be OK having a weekend to herself while you and your husband go catch up with family.