What revelations does Heathcliff make to Nelly of his motivations in Chapter 14?

Heathcliff is not willing to leave Catherine with Edgar, whose love is weak, and who is unfit for Catherine's love. Heathcliff laughs at his marriage to Isabella, who in her lovestruck blindness thought him a romantic hero; she has since learned better, but Heathcliff likes to taunt her with her foolish passion, completely unrequited by him.