Ellen goes to see Isabella in Chapter 14, and it is clear by her exchange with Heathcliff during this visit that Heathcliff has no love for his wife and is disgusted by her weakness. He is still obsessed with Catherine and will not believe that her illness will be worsened by seeing him.
As Ellen approaches the house, she sees Isabella looking out of the window as if she is waiting for her, but when she sees her, she draws back "as if afraid." Ellen enters without knocking, and is appalled at Isabella's appearance;
"her pretty face (is) wan and listless, her hair uncurled...probably she had not touched her dress since yester evening."
Heathcliff is sitting at the table; in contrast to Isabella, he looks quite well. Isabella comes forward eagerly and greets Ellen, holding out her hand to take the letter she expects from her brother, but Ellen has no letter. Instead, she verbally relays the message that Edgar sends his love and pardon, but thinks it will be better if he not communicate with her and her new household anymore.
Isabella withdraws in disappointment to sit by the window, but Heathcliff immediately asks about Catherine. Ellen tells him that she is recovering from her illness, but is much changed; when Heathcliff asks to see her, Ellen tells him that such a visit would kill her. Heathcliff is convinced that Catherine still loves him, and expresses his intention to see her, no matter what. Heathcliff then makes clear that he loathes his wife Isabella; he is disgusted with her weakness and perversely delights in tormenting her. He says he never did anything to make her think he was a good person, but she insisted on remaining "under a delusion," and so her misery in her current situation is her own fault. Isabella, on her part, has learned to hate Heathcliff, whom she says married her to obtain power over her brother Edgar. She declares that now, all she wants is to die or see Heathcliff dead, at which point he thrusts her from the room.
Heathcliff asks Ellen to help him see Catherine, telling her that he will do so whether she helps him or not. He is convinced that, despite what anyone says, Catherine wants to see him, and has "no doubt she's in hell among (the Linton household)." Heathcliff prevails upon Ellen to deliver a message from him to Catherine, asking her directly if she wants to see him, and, despite her misgivings, Ellen finally relents (Chapter 14).