Hi Beth,
My parents are both dead now, and my dad, who was the true n in my family, died 3 years before my mother. My mother and I were very close after I got through my difficult teenage years, and became close friends and companions. I was living in another state, but would call her several times per week to discuss everything that was going on in my life. I would rarely have any conversation with my father, and if he answered the phone, he would say hi and hand the phone to my mother, without so much as asking how I was doing.
After I moved back to my hometown, I was spending more time around my father and he was getting older and even more difficult than he always had been. I was older, stronger (emotionally) and more confident in my ability to stand up to him and defend myself verbally. I would not only stand up for myself, but also to the constant attacks he made on my mother. She was always a weak woman, who completely deferred to my father and his wants and needs. The more I tried to defend her, the more she took his side and made me out to be the bad guy. I finally had to give up on both of them to save myself and my children from being subjected to my parents' constant bickering and my need to fight with my father.
So, I completely understand your dilemma and conflicted feelings of wanting to stand by the non-n parent who has learned to adapt to the life of misery of living with the n, by becoming more like them. My response was to totally walk away, so I don't have any better coping mechanisms to offer you, I'm afraid. I have spent most of my life searching for Jimmy Stewart. I don't know that I will ever find a father replacement--no matter how hard I try.
I wish you well.
Brigid