[Dr. Lecter]

Remember this first: In a marriage, you have committed yourself to work things out together. Jumping to conclusions is unhealthy.
Difference between a marriage and bf/gf is you are sworn to stay together thru good and bad, or at least try to.
You need to give her the benefit of the doubt with the explanation. After all, there are 3 strikes even in baseball. I'm not saying you have to believe her, but if you have demonstrated that you are jealous of her ex and this event has topped it for her, your relationship wasn't on very solid ground to begin with.