You can infer that Hindley was jealous of Heathcliff when their father was alive.He did not treat Heathcliff well .Hindley started being worse when the father died .Catherine saw that Hindley did not accept Heathcliff as a brother because he tought Heathcliff took his father away from him.Because of that he was always ill treated by Hindley and then Heathcliff became revengeful.
