How does cruelty play an important role in the destruction of love and in the novel as a whole?

Cruelty runs through the novel. The cruelties Heathcliff suffers as a child and adolescent harden him. He is adopted, favored by his stepfather, and then, after the stepfather dies, he is abused and degraded by his stepbrother. He and his stepsister Catherine develop a strong bond and love each other, but Catherine treats him cruelly when she marries the wealthy Edgar Linton rather than him. Heathcliff also suffers when Catherine dies.
Because of how he has suffered at the hands of the Earnshaws and Lintons, Heathcliff wants revenge on the two families. Therefore, he treats Isabella Linton, the woman he marries, with sadistic cruelty, wanting her to hate him. He also mistreats Cathy, Catherine and Edgar's daughter, after he and Isabella manipulate her into marrying their son.
Bronte shows how abused children become abusive adults.