My fiance's good friend's wife is throwing a surprise birthday party for her husband. She sent the invite via Evite and invited my fiance. No "spouses and significant others welcome" or anything like that. So we debated as to whether I'd go, since I would hate to show up at something that I wasn't invited to. We both assumed she didn't mean to exclude me (and other significant others), and I finally agreed that I'd go with my fiance. She is a very nice girl and we both thought she'd be surprised if I didn't go because I assumed I wasn't invite.
Fast forward to literally 10 minutes after I agreed to go. She updated the invite to say "please feel free to bring your spouses." To which MY fiance got a little irritated, since he felt like she was now excluding any significant others who are not married. We now both agree that she probably just doesn't understand etiquette (this isn't the first time she hasn't followed the right etiquette path) and that she doesn't understand what she's saying.
So, would it be rude of me to go even though the invite was pretty specific in that only spouses were invited? Or, should I go with my intuition and attend with my fiance because I don't think she is intentionally being rude? I really want HIM to go since it's his good friend (yes, I know he can go by himself).