I think while it may be possible for an abuser to change with a lot of therapy and a strong will to do so, that it may be made more difficult for him to do so in the same relationship where he was the abuser. There is a certain dynamic there that is very difficult to change. My dad abused my mom who eventually left him. It wasn't until decades of accepting his losses and therapy and the desire to change that he actually did so. I seriously doubt he would ever have stopped if my mom had not left him.