(aka "someone needs to read Miss Manners/Emily Post")
There are two people, let's call them Partner A and Partner B. They've been together for a long time - let's say over 20 years. Not married, not living together, but definitely a couple, and usually treated as such. For example, when Partner B's family was being honored, A was invited to the celebration. When A's family has events, B gets an invitation (and vice-versa). A is included on B's family e-mail list. Etc. Invitations to a Major A Family Event recently arrived, one to A's home and one to B's. And another invitation to a Major B Family Event came to B's home addressed to "Partner B and Partner A".
So why, after all this time, does an wedding invitation arrive addressed to "Partner A and guest"? I think that means that B isn't invited... or am I wrong?