We're mailing our invitations this week.  I think I might burst from the excitement! 

We're inviting everyone with a guest, and I'm certainly set with the married couples and unmarried couples living together; but I'm a little stumped beyond that.  For the single folks, I know I can write "and Guest" on the inner envelope, but I may go with just the one person's name and a hand-written note that says he/she is welcome to bring a date.  Here's where I really need help: someone in a relationship but not living with the significant other and whose significant other would not be invited without said guest.  Know what I mean?  

My fiance has known X for years, and they're good friends.  X is dating Y, and while we're all friendly, should X and Y break up tomorrow, we would invite X, but not Y.  Since X and Y don't live together, if I were truly inviting both as individuals, I would send each an invitation.  But since I really see Y as X's guest, do I send only one invitation?  And do I address it to X only and then write X and Y on the inner envelope?  I certainly don't want to use X and Guest since I know Y is the guest.  

Please help!  Bride brain has set in, and I'm obsessing over details I'm sure no X, Y or Z will ever notice.  :) 

If I were X and had been dating Y for years (and know that you know both of us) and received a invitation with an "and guest," my reaction would be, "Really? You suddenly forgot my boyfriend's name? Or you think I'm bringing the secret man-friend?" :)