Cheating: is my life falling apart?

Stephanie. • Military wife. Pregnant with baby #3!
This is hard for me to share but I need advice even if it's mean. I want to hear it all. My SO and I started off very rocky with him lying and cheating. We worked through it and he has made great efforts to change. We weren't serious or even living together when this happened. Tonight he just told me about another time. It was days before we moved in together and he apparently received a blow job from a girl after a rehearsal dinner he attended in the same hotel where we were staying. This happened over a year ago and I am hysterical. I feel disgusted with him and I want to leave. I'm 16 weeks pregnant and I feel like my life is falling apart. Am I being irrational because I've already been the idiot who forgave a cheating liar and I need to rise above and move forward for this baby? Or do I have a huge right to want to leave and feel like this is the last straw?