I'm not sure how easy it would be for Rob to change. Coercive control is his 'modus operandi' and he has now turned it back on Henry. We got a hint of this from the time of Helen's trial.
If you remember, Helen did not attack Rob whdn he raped her. It was when Helen decided to leave Rob and had packed a bag. While she cooked dinner, she told Rob and he took a knife and challenged her to kill him as this was the only way she would be able to get rid of him. He then seems to have run past her to get Henry and she took the knife and stabbed Rob.
While Helen was in prison and Henry was with her parents, Rob failed to return Henry after the first contact.
It's not Henry he wants but Jack and he will be prepared to destroy Henry, Helen and anyone else who gets in his way.