How can I forgive a cheating wife again?

(Long Question) About a little over a month ago I asked a question on this site about my unfaithful spouse who cheated on me with a college student multiple times unprotected that she worked in the airport with. She is 31 he is 20. I found out she was cheating when I found a card from him in her purse on Christmas night. She would admit to how far they went a week later and said she was sorry and regretted that she did it and that is was a bad mistake. I fully admit I was not there for her enough emotionally as a husband or even as a father of our 2 very young children ages 2 and 3 and know this was her last cry for attention after multiple attempts to work it out with me. She told me she that she had felt that I did not love her and that she moved on without me when she did it. We have decided to start over and rebuild our marriage and it has been amazing the progress we have made in such a short amount of time. I still feel a lot of pain and have a lot of trust issues with her but to come as far as we have in a short amount of time and to both feel the love for each other as when we first got married is amazing. I always used to believe once a cheater always a cheater but now I realize that it may not always be the case. Anybody who knows her and had grown up with her would tell you that this would be the last thing especially for her to do. There were a lot of other issues compounding in our lives besides our troubled relationship and it basically broke her down to where she did commit the adultery. This is one of the major reason I stayed to work this out with her along with taking care of the kids. Today I should not have but I was looking through her email record. She told me during the time I first confronted her that she had sent him an email breaking off the outside of work contact and the ual relationship and that they would only be work friends. I found this letter in her sent history today and it hit me like a ton of bricks. she wrote to him back then that she was in love with him even if she knew he did not feel the same way. She wrote even though she did not want to end it that they could not have anymore because he was not fully committed to her as he had an girlfriend and maybe some other partners. She admitted to him that she never believed in non emotional with anyone as I was her first but that she enjoyed being with him in that manner and would always have an attachment to him. She also left it open that if he changed and fully committed to her she would chose him over me. She emphasized to him she had to remain friend to him because it would crush her if they did not. The bottom line is that although she cared for me she cared for him more and felt as if she was settling for me because I offered long term commitment. As the story goes he showed his true colors and basically abandoned her. She now knows what she always deep down knew and admitted to me she probably needed a slap in the face by reality to rejoin reality. I am still disturbed that although he rarely comes around to her store nowadays he still texts her on almost a frequent basis. She has let me know what some of the texts are and they are mostly harmless stupid texts. But it still bothers me that she still responds to most of them. What am I to think I know she wrote the email to him after I confronted her and that basically I caught her and she was still emotionally attached to him. I know she still has a slight connection to him but now also has some resentment towards him. Things are going great now and I know that she may not have been in love with me at the time of the email that she is in love with me now. Do I forget the email as emotional carryover as I know how she felt when she wrote it? But then how can I forget that basically I was nothing more than a settlement at the time she wrote it and if he was not such a uncaring piece of slime that she would have chosen him over me?