We're at a stage of life in which most of our friends are either married or paired off, but a few have remained persistently single. One of these singles recently requested a 'plus one' to a dinner at our home. Of course we said yes, but afterward we worried that we should have invited him to bring a date from the start. What's the etiquette around inviting single friends?
You're under no obligation to provide an automatic "plus one" for your single pals.
Presumably you've included your male spinster friend on your guest list because you think he can hold his own – and make some interesting conversation, even – in the mix of people you've amassed. That said, if he has the fortitude (or, as the Emily Post types might call it, insolence) to ask if he can bring an uninvited guest, you're right to oblige him.
And either way, if all your other guests are marrieds, do at least split them up at the table and try to limit the conversations about mortgages, Febreezing, how nice it is not to be single and all those embarrassing married-people smells.