Am I Overreacting?

I am married to a narcissist man. He has left me three times during our courtship and marriage. The first time he left me was the day before thanksgiving about a year into dating. He tried sleeping with other women. The last time he left me was a month after we were married. He was hot for a girl at his job who just turned legal age and he tried to sleep with her, as well as over 100 other women. He swears he only tried sleeping with other women but nobody said yes (he's not the best looking man but he can be very charming with attention and gifts at first). So basically, he never physically cheated (according to him). However, thru therapy and stuff it was decided he would not even talk to other women or ever get in a car with another woman & etc. Last July he was injured at his new job, cut his fingertip on a machine. A 25 year old woman (he's 34 but looks 40) drove him to the ER and even sat with him in his private room until I got there. I was mad as heck! I yelled at her and talked to him about how inappropriate that was. We discussed how tempted he would be to talk to her at work from then on because of the attention she gave him. Since then he had promised he wouldn't talk to her and if she tried to talk to him he would walk away or tell her he couldn't talk. Well, I'm 4 months pregnant now and I found out last month that they've been talking at work about everything from marriage advice to work stuff. I was devastated especially because it was so easy for him to deceive me and betray me. I found out because she reached out to him on Facebook. Well, since then they got into an argument at work and they both said they weren't going to talk to each other ever again. 
So here's where my question comes in: I found out she came up to him yesterday and asked him where the boss was, he answered her and said which way the boss went. I feel betrayed again because he agreed never to speak to her again and they don't work in the same dept. I feel he should have reminded her that he can't talk to her. Am I overreacting? Almost every time he has admitted to something there has been much more to the story that he's left out. I'm very concerned and I know he's never going to change but I don't want to be a single mom again. I'm devastated. 

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