Sirona:
I would imagine that each is affected differently, depending upon many factors, such as personality, intelligence, the importance of religion or a religious view in their life, the importance their mates religious view is to them, whether or not there are children involved, how much the person really knows about JW beliefs, doctrine and history, and so forth.
As an unbelieving mate of a JW, I can tell you that it does take its toll on me. The toll is mostly emotional: Sadness that my JW wife is a religious bigot and I am the object of her bigotry (even though she doesn't realize this or refuses to see it); that our relationship suffers because of this; that there are many levels where we just aren't going to communicate - we're out of synch in so many ways. Fear that our son may be indoctrinated into such a black and white, we vs. them world view; that he will lose his precious spontaneity, curiousity, and enthusiasm for life; that one day I will be the object of his intolerance.
My thinking has been affected, but not towards a view more similar to a JW. No, I don't see religion, JWs, or most anything for that matter, in black and white terms.
I would imagine that each is affected differently, depending upon many factors, such as personality, intelligence, the importance of religion or a religious view in their life, the importance their mates religious view is to them, whether or not there are children involved, how much the person really knows about JW beliefs, doctrine and history, and so forth.
You don't explain much about the situation with your stepdad, but the JWs aren't wrong about everything.
Take care,
CPiolo