I have been writing romance novels for 20 years now, and I have frequently had readers tell me they “fell in love” with one of my characters. I fully understand that because I have unfailingly fallen in love with each of the heroes of my books.
We are all flexible and we all have multiple facets. So I could be as completely happy with my superstar entertainer, Darryl Bridges*, in one scenario as I could with my country preacher, Tyler Barnett**, in another.
We all have imaginations to some degree or another; else there would be no movies other than documentaries. There would be no such thing as fiction in writing. Fiction is by definition a function of imagination.
When the author’s imagination taps deeply into that of the reader is a situation in which a person could fall in love with a fictional character.