Spending years having that feeling that you need to 'walk on eggshells' around someone to keep peace in a home really wears away at you, doesn't it? I spent many years with my ex-husband (not an A) feeling the same way simply because his personality was so mercurial. He ended up having an affair and divorcing me...which was a gift to me in the long run!
I can't tell you to stay or go. I can tell you that your peace, your happiness matter...the safety and peace and happiness of your child matters, too. How best that can be achieved, I don't know. But at the base of it all, perhaps that is where you can begin to make decisions.
Come here and vent all you want. We are walking this path with you...and I'm so sorry for all you and your whole family have been through.