character being evil

"But, for all that, I was not going to sympathize with him- the brute beast."  This was said on page 148.  In this quote, Isabella came to Nelly asking for help.  She was complaining and worried about her life with Heathcliff.  He was not treating her well at all, and basically just treated her as his servant.  She also was terrified because Heathcliff and Hindly have been fighting almost every day recently.  Isabella has lost all respect for Heathcliff.  I think now that Heathcliff has just turned evil.  I do not think originally he was evil.  In my opinion, Hindly treating him so cruely as a child made him this way.  The only reason Heathcliff married Isabella was to get his revenge on Hindly and Catherine.  He never loved Isabella!