At one point in Emily Bronte's "Wuthering Heights," Catherine frantic as she searches for Heathcliff, answers Nelly's inquiry into her state of mind, "I am Heathcliff!" Later, as Heathcliff mourns Catherine, he makes a similar assertion: "I cannot live without my life!" Thus, as David Daiches in his introduction to "Wuthering Heights" observes, there are Heathcliff's "natural claims to Cathy" in conflict with the "artificial claims to Cathy" by Edgar Linton. That is, the passionate bond that Cathy and Heathcliff share is not like the bond of cousins and the marriage of those in the same social state.
But, just as in "Romeo and Juliet," the "violent delights" of Heathcliff and Catherine have "violent ends"; no relationship can withstand the denial of its passion. Catherine's marriage to Linton is doomed, especially when Heathcliff reappears to take what passion in her nature remains.
In the novel 'Wuthering Heights' by Emily Bronte, Catherine thinks she loves Heathcliffe, but marries Edgar Linton nevertheless. One interpretation of this is that Heathcliffe is aligned with her childhood self whereas Edgar Linton represents her matronly, or adult, self. In a way, Catherine's clinging to childhood passions and values such as disinhibition, freedom of movement and freedom from responsibilities and consequences is rather idealistic, unrealistic and immature. Her love of roaming the wilderness and frivolous pursuits so frowned upon by the old servants could not go on for ever and a part of her knows this. So, realising that Heathcliffe is not a realistic prospect for a conventional future, she marries conservative traditional Linton - but her soul is still restless for the other part of their old selves.
In the book "Wuthering Heights" Catherine is more true to her nature when she is with Heathcliff. She is able to be free spirited and challenged. Catherine and Heathcliff have a sexual and emotional passion towards one another. She feels like she is one person with Heathcliff. He is her soul mate.
Catherine with Edgar is more structured and civilized. She is more materialistic and worries about what others think. She behaves more the traditional female and is also moody and depressed. Catherine follows more the pomp and circumstance of a woman of her day. Her love for Edgar is more related to his kindness and good treatment of her than passion. She feels obligated to Edgar.