My ex fiancé cheated on me after 4 years... right before we were to get married with her best friend’s boyfriend. I literally caught them in the early morning hours sleeping in my bed after coming home early unexpectedly. I literally said nothing to her... grabbed some friends, rented a truck, and was packed up and gone by noon and never spoke to her or looked back.
I think I would take it as a sign that the relationship is probably over and work towards a peaceful resolution of the relationship. If she thinks we can make it work, then maybe we can sort it out. Ultimately though, it should end at that point.
If I expect and or deserve another chance, so does she. However, if I do not, then she does not either. And she better not be pregnant, because she is done with that pregnancy...
I have no fear of that happening now at all...but I have had it happen before and I gave a second chance only to be made a fool of. IF it were to happen again there would be no second chance this time.