Unfortunately one is too many and for a woman in relationship with a sadistic man life will only get worse. Like an addiction if untreated it is way to hell for the partner. As for the man he has certain personality traits that probably developed during adolescence or even earlier. Some form of abuse in his childhood has lead to parts of his brain that develop empathy not to develop so there is a gap in what the perpetrator feels about himself and the other person. For some it is even worse in that they get pleasure out of other’s suffering. Often they are manipulative looking for some power and control over the other. Having felt they were ignored as kids they are narcissistic looking constantly for recognition. Their thinking is negative so they pour scorn over everything.
This is a bleak picture. There is evidence that these men can be treated if they are motivated which is not always easy until the man has hit the wall. And for some even this doesn’t work as they are fearless of consequences and like to play life to the edge. As individuals they are very isolated emotionally. They compensate by talking very quickly, get obsessed in work and frequently fantasize.
What is sad is that some women feel an attraction to these guys, then the relationship gets compounded by the advent of children and so goes to the next generation. Mindfullness and meditation are the obvious antidotes to the sadistic mindset. The loving kindness meditation where the individual wishes others he likes well, then wishes some one he has tension with well, the world well and himself well can stir up new neural connections to move them out their trapped thinking.