I'd play this more LAG:

I'd like to know why you are cheating on me....

I seen you with him the other day when i went to drop by...

Looking a bit cosy with him....

Also sorority, maybe shes getting into girls [img]/images/graemlins/grin.gif[/img].

If she flips out on you, just say you were kidding [img]/images/graemlins/confused.gif[/img] ??

I dont think she will fold at all though, women think they are too clever.