Wife or 3 weeks caught in a bad lie

I just found out that a guy my new wife works with was once a fling, we have been together for 3 years and we just got married a month ago, I have asked her if there was anything between her and this guy before because of the way he acts when I am around, she always says no I have never had anything to do with him, she swore. Ive asked her more than on one occasion during our time together and she aways says no. the night before our wedding her friend made a comment about something and I kinda put two and two together and 3 weeks later asked her again and once more she denied it, then she said they just went out and it meant nothing, then I kept asking and she finally admitted they slept together when they were drunk. They work alone together at night in a hospital same room. Should I be pissed, I mean she lied to me her husband and she continued to lie, I even asked her on the night before our wedding if there was anything she wanted to tell me and of course she said no. Who wouldn't be upset about this. I understand the past is the past but This is not part of her past when she is still seeing this guy at work and textin and calling him. Im not sure if I can get passed this. I hate liars, the first month of marriage and this comes out, it should of came out before we were married she had plenty of time to come clean. What would you do? I should mention they did the deed over 5 years ago. so she says

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