Yeah, I realize now there should have been some sort of contract, but at the time, the person was a personal friend and never thought there'd be an issue. I never discussed ownership of the images with the client, I just assumed that as a photographer shooting art, I would indefinitely own the images and they were using the particular images for the one instance of the book.
The projects were definitely separate, I got paid separately for the first 3 books.
Deals with "friends" are the most in need of a written agreement so friends stay friends by just following the written document without all the drama of he said she said.
Yes, I definitely realize this now. Thank you for your advice.