Correct me if I am wrong, but I thought giving yourself better accommodations your guests was a faux pas? You wouldn’t serve yourself champagne and give your guests grape juice, or eat caviar when your guests are having hot dogs. Does that only apply to food? I know it is her party and her tab, but something about inviting only her SO seems off to me. I just can't put my finger on it.
Personally, i would be a little put off. I don't like those one-gender-only events. I just don't. If i participated in one to help my friend celebrate her birthday and found out it was only SO-free only for some it would leave a bad taste in my mouth. Maybe i am petty, i don't know.
That's a really good point! If you remove "boyfriend" from the equation and say "Zoe has stated she's got limited funds so she's paying for X for herself but not her friends because it's her birthday and she's hosting. Is that okay?" I wonder if more people would say "You need to accommodate all guests equally and plan the party accordingly." ?
I see the boyfriend as another equal guest, not a special accommodation or privilege for Zoe. I guess that's where my disconnect is 
And that would have been the case except the cat's out of the bag. Its already been said that the reason the others SOs aren't being invited isn't because they aren't friendly with the group or wouldn't normally be part of things. Nope. Straight up its cause she doesn't want to pay for them. And its already been said its a "girls" thing. Once you say those things you can't really say "well no it was always going to be this way this is simply a gathering of my closest peeps." 'Cause its been made clear that's not the case.
I also think that gender isn't what makes for a changed atmosphere, its romantic rel
ationship. A random guy-friend of the group? He's still just a friend. But this is a
boyfriend. And that does change dynamics. And I know lots of people say "well when my SO & I hang out its just hanging out, its no different it doesn't change the atmosphere!" and I say to you: you are deluded. Because it
does. Not for better or worse necessarily, but it is different. And if its not different then they aren't really a very "significant" significant other then are they? Maybe there is no romance whatsoever in your rel
ationship then. Because being "significant" and being a "romantic" partner are what makes for the difference. It might be subtle but it is there. Because its no longer a group of equals - where everyone is simply platonic friends. Now its a group of platonic friends and a subset of romantic friends.
