This "what could have been" can be a real bugaboo. But eventually she'll realize that she's completely content with you.
I think sometimes just the fact that they've thought about someone else is enough to have them doubting their feelings for you. You are in a great position though Brit...and I think it's better that she tells you about it you're willing to listen. I don't know if guys & girls think differently on this one...but I would rather know than not know. Plus, she's probably feeling you out a bit when she talks about it. To see your reaction.
Have fun at dinner. J~
M 35 H 29 M 4 yrs T 9 yrs D 3 S born 10/19/07 Bomb 09/10/07 Separated next day OW - broke up and H moved out 09/07/08 Status - still figuring this out