How does the rivalry with Linton affect Heathcliffe?

Heathcliff's rivalry with Edgar Linton brings out his dark side. He despises him so much that he marries his sister Isabella simply in order to gain revenge on Edgar for marrying his beloved Catherine. Heathcliff is clearly eaten away by hatred for Edgar, so much so that he's prepared to subject Isabella to a loveless marriage simply in order to settle scores.
Yet, as is so often the case, revenge doesn't provide resolution. So long as Catherine is with Edgar, Heathcliff's soul will remain in a state of almost permanent torment. This torment manifests itself in acts of physical and psychological abuse towards Isabella, who bears the brunt of Heathcliff's loathing for Edgar.
Heathcliff's rivalry with Edgar also seriously impairs his judgment. He knows that his son, Linton, is better off at Thrushcross Grange than at Wuthering Heights, but he so hates the idea of his own flesh and blood being raised by Edgar that he demands him to return his son so that he can raise him himself. This turns out to be an utterly disastrous idea. Heathcliff clearly has no time for this "whey-faced, whining wretch" as he calls his son, and is temperamentally unsuited to fatherhood. But he's so utterly blinded by hate for Edgar, so bitter and full of pride, that he either can't see this, or chooses not to.