How do I fix It? I lied and got caught

I created a secret social site page in an attempt to see how old friends have been doing and got a hit from a girl I had sex with. My fiancee found out and busted me red handed, but I chose tolie because I was scared she would be so upset she'd leave me and call off the wedding. Now she wants to talk to a guy who she had strong and I mean strong feeling for at one point and its all because I chat with a girl who I had sex with. She no longer trusts me and she is really hurt. I know I was wrong and just want to fix it. What should I do???