Brother/Sister (?)

One of the oddities of Romanticism when Bronte wrote the book was the preoccupation of writers like Shelley, Wordsworth, etc., with androgeny and the taboo notion of brother/sister love. Simply put, Cathy and Heathcliff are raised as brother and sister and can never be a real couple. Cathy herself says, "I am Heathcliff." Notice in the novel who astonishingly similar their anger is. If you want to read about this, consult the book "Sexual Personae" by Camille Paglia. She is a scholar and literary critic. The book is fascinating on this topic.

The novel does not explicitly state so but strongly implies it.

We can probably thank Lord Byron as the theme is rare in Western literature before he arrived on the scene.

Prior to that, we have to go back to the Greeks, Romans and of course, the Bible.

I am currently reading the novel and the introduction by Daphne Merkin includes this paragraph:
<<<<But by far the most intense psychological scrutiny was reserved for the close relationship between Branwell and Emily (Bronte brother and sister). After Charlotte (their older sister)had given up on him as a bad egg, Emily continued to stand by her older brother, calming him down and getting him to bed during his drunken outbursts. This aspect of the Bronte family life led to speculations about a possible incestuous aspect to Branwell and Emily's relationship, especially in regard to it's being the model for the relationship between Catherine Earnshaw and Heathcliff. (One theory suggested that Heathcliff was in fact the bastard son of Mr. Earnshaw and thus Catherine's half brother.)>>>>>