Reach down to the patch of flesh under your urination device. Shake the magic 8 balls and see what they tell you.
I disagree with those that have a problem with her going out with her girlfriends to bars. Once in a while, going out with the girls is HEALTHY for a healthy relationship. If she's loyal, it won't hurt a damn thing. When new dicks start swinging around, thats a sign of trouble that doesn't need a Bat-light to be seen.
The fact that you're posting this, tells me your caveman instinct is that something is going on. Unless this isn't the entire truth, its time to blow that tugboat out of the water.
If it will help your decision, I guess you could smell her belly for Old Spice and stanky-semen after the movie.