My own life bares this out in that my father bailed on my mother because she developed scleroderma, a painful and disfiguring auto-immune disorder. He cheated on her openly then divorced her on the basis of her alcoholism, which you could do in those days.
I long ago promised myself that I would never be such a coward. If it ever comes down to something like that in my own life then I will know for sure what I am made of.