Ok so here's what happened:
I was engaged to be married to a beautiful girl whom I've been dating 3 years with few problems. We were supposed to get married in June of this year, but then in December she cheated on me. The cheating entailed making out with this guy and very light petting. (she grazed him outside his pants and he tried to feel her up but she stopped him) I chose to forgive her because when she cheated I had been neglecting her for some of my friends. I pretty much never got to see her, and I blew off our dates, etc. We were fine except this pain was killing me... But the wedding was still on and we were going to make it through.
Now the problem is I cheated on her. I am pretty sure I did it just because she cheated on me, but I don't know. I had faith that she wouldn't do it again because she came and told me the next day what she had done. Now I've gone and done worse. I made out with this girl in her car and there was very very heavy petting... meaning inside the pants and shirts and all that.. I don't know what to do now because to be honest, I really liked the other girls kiss, but I love my fiancé more than anything in the world and I don't want to screw up our wedding.
Should I tell her? Or should I keep it a secret? Should I cut off all contact with this other girl? Or should I just play both until it blows up in my face? All advice is appreciated! Thank you.

