He not only degenerates mentally but also physically, as he is seen having fits, and spiritually because he is prepared to deviate from the strong Christian social conventions of the time, and commit the sin of murder. So, he ruins his entire life, destroying his mind, his body, his morality and social standing all from the passion derived from his jealous.
Likewise, Heathcliff life is also the ultimate victim of his own revenge. He is angry with Hindley for the misery Hindley caused him when Heathcliff was a boy. He suceeds in his revenge against Hindley, owning all his property and gains control over his son Hareton. Heathcliff is able to corrupt Hareton, letting him run wild and uneducated. But although this provides him with some satisfaction, his association with Hareton only serves to torment Heathcliff further, as he himself admits "his (Hareton) society is of no benefit, rather an aggravation of the constant torment I suffer" because of Hareton's startling likeness to Catherine and the fact that as Heathcliff himself says " Hareton seemed a personification of my youth" which remind him of what he has lost whilst in the pursuit of revenge.
His treatment of Catherine also goes sour for the same reason, she only serves to reminf him of her mother, who he lost in the pursuit of revenge.
The loss of Catherine is cause of Heathcliffs torment . Through the first half of the book the idea that he and Catherine are twin soulss is constantly prented, both by him and Catherine, who says " I am Heathcliff". They feel they cannot exist without each other. Catherine says "But Heathcliff through his actions towards Catherine after his return, forces her to make a choice, and in the end she carries out her own petty revenge, declaring " I"ll try to break their hearts by breaking my own". And so she dies, leaving Heathcliff alone in the world without his other half, a victim of the jealousy that drove him to instigate her decision.