hmm.. seems to me she is taking full advantage of having the current "upper hand" in the relationship. Forgiveness is a choice even if it isnt always a feeling. When you choose to forgive someone, you are agreeing to work through the aftermath of a mistake as a couple (even if the mistake is as awful as cheating). The bottom like is this: choosing to work through something together is NOT the same thing as continuously punishing someone for a mistake. She sees you are making all the effort you can, and she is still saying its not enough? Well, if your best attempt at repairing the relationship isnt good enough, that only leaves one alternative, doesnt it?
I have a feeling this relationship is toxic and headed for break up anyway. I personally wouldnt tolerate the cheating OR the use of guilt as a form of control.
Side note- I am willing to bet that if you stood up and told her you were ending the relationship due to inability to repair damage caused by your mistake, this entire situation would turn around...