Well, she sent the text because she wanted to send it and it is about making herself feel better. So, don't take it personally. That's the point of DBing. Don't read into any of what she does. You might be right. You might be wrong. But you never know and it doesn't matter.
As for forgiving yourself for not being more aware of the severity of your marriage's problem, there's no sense in looking back on things. It doesn't help and we all make mistakes. And I'm not sure that the problems were unresolvable before OM came onto the scene. In my sitch, we were doing fine a year before BD. Things started to go downhill toward the end of the year and I think that OM coming onto the scene was a big part of that. I bet it is also true in your sitch. Of course, none of that matters either. Just now and tomorrow.
As for conflict avoidance, I made that mistake too and it isn't always NMMMNG. In a marriage with love, folks don't want to fight and they put conflicts aside in order to keep the peace. But I haven't read NMMMNG.