Quote 1
"I seek no revenge on you," replied Heathcliff, less vehemently. "That's not the plan. The tyrant grinds down his slaves and they don't turn against him; they crush those beneath them." (11.51)
Though Catherine perhaps deserves punishment for turning against him, Heathcliff would do no such thing. What's notable here is that Heathcliff recognizes a pecking order: people pick on those beneath them.
Quote 2
He had the hypocrisy to represent a mourner: and previous to following with Hareton, he lifted the unfortunate child on to the table and muttered, with peculiar gusto, "Now, my bonny lad, you are mine! And we'll see if one tree won't grow as crooked as another, with the same wind to twist it!" (17.119)
With Hindley dead, Hareton is left to suffer under Heathcliff. Like others who fall victim to Heathcliff's abuse, Hareton is a proxy for his father. That Hareton breaks the cycle is a reflection of his love for Catherine and his own strength of character.
Quote 3
"Come in! come in!" he sobbed. "Cathy, do come. Oh, do—once more! Oh! My heart's darling, hear me this time—Catherine, at last!" (3.83)
Just a glimpse of Catherine would assuage the long-suffering Heathcliff, who believes in communication beyond the grave. He is far from afraid of ghosts and has clearly spent a lot of time trying to get Catherine to haunt him.