Jesus sake...LEAVE HER QUICK!!!!!!
You deserve better than that. I'm sorry, but she made her choice and it was not you, it was the other man. You're a good man for allowing her a second chance, but now she is taking advantage of you, your love and your kindness.
You want to marry a woman that cheated on you, and is still keeping contact with that same man, are ya nuts? She wanted to keep a "friendship" with this man...yet she hid it from you? BULLCRAP. She was cheating on you AGAIN, hence the hiding. You don't hide anything that is JUST a friendship. If she truly loved you, then she would have had nothing to do with that man EVER again.
Dump her, quick fast and in a hurry because she is no good and you deserve more than a woman like that. She does not love you, she doesn't care about you, nor respect you. She will only continue to hurt you, if you stay with her. Get rid of her, and if she comes crawling back to you once she realizes how good you were to her, DO NOT take her back. Find someone that deserve you, that will be good to you.