What is another word for a person who loses admiration/love/respect towards someone or the act of losing said traits?

I am looking for a more educated word than "Hater" that describes a person or type of person that at one point admired/respected you, but then for one reason or another, ended up hating/disliking/attacking you. Not necessarily betrayal either. Its more about the part where their emotion/mindset is going from admiration/respect/love to belittling/disrespect/hate towards a person. Adjectives are acceptable too.

A word for each scenario that it could be used in:

1. You reject their love/admiration so they start hating you/attacking you instead
2. You don’t live up to their expectations so they don’t admire/like you anymore
3. Doing something that changed their initial impressions and feelings about you