Here's what's behind her blaming you and re-writing history: she knows she's doing something she shouldn't, she knows she's wrong, but at the same time, what she's doing is really exciting and makes her feel really good!
That's a bind -- she shouldn't do this, but she can't help herself from continuing.
When that happens, people will initially beat themselves up and feel very guilty for what they are doing, but human nature is that you can only feel bad about yourself for so long and then a preservation instinct kicks in.
When that happens, it goes something like this: "I'm doing a bad thing, but I'm not a bad person. So if I'm not a bad person, someone else must be *making* me do this, and *they* must be the bad person"
Since you're the only other one in the relationship, they'll latch on to you as the cause of the problem, and will then re-write history, invent things, and look for any little thing you do that supports they stories they are telling themselves.
It is a very sophisticated form of self-hypnosis so that they can justify and continue their behavior without the attendant guilt they had been feeling.
If you're then remorseful, apologetic, and pursue them, it reinforces that you must be acting this way because you did something wrong, and it makes your situation even worse!
Your very best move here from a psychological perspective is to completely go the other way. You leave her versus her leaving you. Don't accept anything she's telling you about this being your fault, just outright reject it. Don't compromise on that, don't think you'll be a nice guy and meet in the middle, feel free to make her angry. She needs to believe that you consider yourself to be more valuable than the treatment you've been getting.
You need to establish your value, by not allowing yourself to be in a relationship with someone who is not faithful. You can't control what she does, there's no way you can do that, but you CAN control what treatment you will and will not accept.
Moving away from her emotionally is scary and seems counter-intuitive, but its absolutely the best move you can make.
Think back to dating -- who is more intriguing to you, a person who easily falls into your arms, or a person who is hard to get? Which one is more attractive?
Married 18, Together 20, Now Divorced M: 48, W: 50, D: 18, S: 16, D: 12 Bomb Dropped (EA, D): 7/13/11 Start Reconcile: 8/15/11 Bomb Dropped (EA, D): 5/1/2014 (Divorced) In a New Relationship: 3/2015