Well, my H would have said our marriage was normal at first, too. It took a while before we BOTH realized that we didn't see things clearly, and didn't take responsibility for our marriage and how it was REALLY going. My H, to this day, still says that it was an extreme shock to find out that I had an affair. I was not that "type". I still am not that "type".
As for her saying "this would have happened anyway"....yeah, she is trying to justify leaving you, and a way to rationalize it. If she doesn't rationalize it she has to look at herself and what she has done.....this is extremely hard to do, especially if she has made one story about you and her to other people.
