I can't decide if him going from poisoning her one day to looking at her with big puppy eyes the next, so quickly, is unrealistic or extra-realistic given the particular sorts of crazy we know he is.
(But if the latter I'd be extremely worried about swinging back the other way on equally short notice :/ One does not simply "get better" from personality or mental-health problems that came from neglect the moment someone starts looking after them. Which is not to say it's not a crucial first step in the right direction, but... Alas.)