i think maybe what you can do is focus on setting boundaries for yourself in your relationship with him rather than trying to change him. unfortunately, we can't change others although it sure would be nice at times. since his niece is family you may be up against a losing battle in trying to get either of them to change their dynamic. you are setting boundaries though regarding what you will and will not tolerate concerning her and that's good. i think if you do the same with your bf you will be happier and see better results than if you try to get him to change.