I have to echo BF and bttrfly's thoughts. I sometimes find myself doing the same thing. Not rewriting history, but focusing way too much on the negative stuff.
I found myself reaching, sometimes going way back, for things h had done or not done and using those to fuel my anger and resentment toward him, as well as reasons to do whatever I wanted or treat him however I wanted. Thankfully, I realized I was doing pretty much the same thing he had done (only on a much smaller scale). I still catch myself doing that from time to time, but have made an effort to stop my train of thought and make sure my thoughts aren't distorted by the current sitch. I want to at least try to think as clearly as I possibly can in the midst of this tornado.
I so wish I had a magic wand to wave and make your MIL issues go away. It's hard enough to deal with a MLCer and protect yourself and your child without having to do battle with his family at the same time.
Me: 59 and holding H: :53 Me: 1 S, 1 D, both grown M: 19 T: 23 BD: 9-23-2013