The essence of Heathcliff's and Cathy's love is that it is doomed. Their passion for each other can never come to fruition, and the death of Cathy and Heathcliffe's incolable passion for her, even in death, forms one of the most powerful lovve stories every written. The story is complex, being told through the eyes of different characters, and it is a remarkably mature and assured work, given its time, and the circumstances of its author. Read the novel again, and then check out the plot overviews available on the web, and see if you can approach it from the angle of doomed love, which is its underlying theme, and its continuing power.