"That is not my Heathcliff. I shall love mine yet; and take him with me - he's in my soul"

This line is a classic example of Cathy being more in love with the idea of Heathcliff than she is with Heathcliff himself. She has a perfect Heathcliff in her head, and she knows how this Heathcliff would act towards her. When the real Heathcliff fails to measure up to this ideal she reverts to the comfort of the imagined one. This fits with the childish, spoilt character of Cathy who cannot deal with not getting what she wants.