Hi, Unfortunately, I have been put in this situation before and it's not at all nice. In the end I went out with my friend and when the other friend asked where I had been, I just said that I bumped in to so and so and we ended up going out for lunch. That way, the friend who hasn't been invited didn't feel as upset because she saw it as a last minute arrangement. I hope this makes sense. Other people who have not been in this situation may say "just tell your friend the truth" but believe me it's not as easy as that so I sympathise with you! x