WOW, I just had this somewhat same situation yesterday! Nadine, my bestfriend (or was about 2years ago) called me up and asked if I would go to lunch with her.
I did, yesterday! I know she is expecting me to have her in my bridal party, I staright told her yesterday (and she didn't even ask if she was in the wedding.) I brough it up.
"I have decided to have Dave's sister Alyssa as my MOH"
Nadine "Oh yeah..."
" At this point I don't feel I have a close friend that I would choose to have in our wedding"
Nadine "I can understand that, I feel the same way about my friendships" (She too is getting married)
" So I have decided to have the two people that are closest to me, besides we are keeping it very small"
Nadine "That sounds great Jayme"
She was very good about it. I know she may have been smewhat upset, but the way I see it...She is my friend and I still care about her and want to be straight-up and honest with her....

It's gonna work out.
Be honest, Will u be inviting them both to the wedding?