I've got it!
One of us calls her with "Ms. Soandso... I don't know how to tell you this, {dramatic pause} but Confucious has been in a car accident. I'm not going to lie.. but it's pretty bad."
Then another of FBG's co-workers says loud enough so your gf can hear "Doctor we're going to need you right away in the OR" to which the original conspirator tells your GF, "I'm sorry, I really must go. I'll call you again after surgery."
Then wait about 15 mins to really get her panicking (especially since no hospital name was given - it would help if there are a few in your area to add to the confusion). That's when you call your GF and tell her:
Hey hey baby how ya doin' come on in here.
Got some hot chocolate on the stove waiting for you.
Listen first things first let me hang up the coat.
Yeah how was your day today? Did you miss me? You did? Yeah? I missed you too. I missed you so much I followed you today.
That's right now close your mouth 'cause you cold busted!
Now just sit down here, sit down here... I'm so upset with you I don't know what to do.
You know my first impulse was to run up on you and do a Rambo!
I was about pull out the jammy on you and flat blast both of you!
But I didn't wanna mess up this thirty-seven hundred dollar lynx coat, so instead I chilled -- That's right chilled.
I called up the bank and took out every dime.
Than I cancelled all your credit cards...
I stuck you up for every piece of jewelery I ever bought you!
Don't go lookin' in that closet 'cause everything you came here with is packed up and waiting for you in the guest room. What were you thinking?
You don't mess with Confucius!
I gave you silk suits, blue diamonds and gucci handbags.
I gave you things you couldn't even pronounce!
But now I can't give you nothing but advice.
Cause you're still young, yeah, you're young.
And you're gonna find somebody like me one of these days . . .
Until then, you know what you gotta do?
You gotta get on outta here with that alley-cat-coat-wearing, hush puppy-shoe-wearing crumbcake I saw you with. Cause you dismissed!
That's right, Silly rabbit, tricks are made for kids, don't you know that. You without me is like corn flakes without the milk!
This is my world. You're just a squirrel trying to get a nut! Now get on outta here. Scat!
Don't touch that coat...
This will give you all sorts of hand, and if she really wasn't planning on cheating on you, she'll do anything to convince you. If she really was looking for a new guy, you make the pre-emptive strike and come out on top. Win/Win scenario.