Wife Cheated, Does Past Sex Abuse Excuse Or Justify It?

Here is the story:

My wife and I lived together for about three years before we got married. We never had any problems that were not solved before we when to bed together. I have never slept on the couch, and she has never run to a friend's house to spend the night (while we were dating).
We were married in March 07, and things changed. She grew distant, cold, and unemotional (things that she NEVER did before the marriage.) I had no idea what was going on. I thought it was just the stress of marriage/new job/etc.
Within four months of marriage she cheated on me twice in one month with the same man in another state. This was a boyfriend from many years ago, that she got back in "touch" with.
To make a long story short, he was caught by his girlfriend because she read his text messages. She called me and told me the whole thing. I immidiately threatened divorce and confronted my wife. She broke down HARD. she couldn't stop bauling, saying she was sorry, etc.
We went to councelling the NEXT day together. Nothing was really found out, since it was our first visit.
Now, I am not the type of person that gives second chances out like candy. Here is why I am sticking around for the time being, and this is what I need help with. I found out 2 weeks before I found out about the affair that my wife was sexually abused by her step-father AND grandfather between the ages of 4 and 9. I had NO IDEA about this. I began reading books and articles about survivors of childhood abuse and marriage. It feels like one book in particular was written FOR HER. The effects of abuse can follow a person around for their entire lives, and have side effects that include feeling empty, feeling emotional dead, needing to feel sexy or loved at all times, not being able to let people down or say no, and having split personalities to deal with issues and guilt. One of the big kickers in the book was that a complete relapse can be brought on by life milestones. We have had a lot of milestones since we became married. We were married, we bought a new car, and we bought a house. These things could have brought back a relapse, explaining why she changed when we were married (all three of these things happened within one month).
Now, one week after all of this she tells me that she wants to move out and be on her own. Her reason is because she has never been on her own, and she wants to feel like an independent person for once in her life. She wants to know that she can make it out there. She says she needs to find herself by moving out, and being independent.
This is very hard for me to accept. She cheated on me, and now wants to move out on her own? She is a very attractive 21 year old woman, I know guys will try to take advantage of the situation, trust me, no guy in their right mind wouldn't want to be with this woman, it's what sucked me in in the first place.
I don't know if I can take her moving away, for this very reason. But then I don't know if keeping her here will help us, or destroy us. I honestly believe her intentions are good, and that she does not want to seek a relationship with another man, but can she and will she say "no" when they seek her out?

I could really use some sort of input on this ordeal. And please, when you respond, try to take into consideration her issues in her past. I honestly believe that they are playing a huge part in our problems.

Thank you,
~B