You're a trusting soul, Reg. I learned years ago not to "loan" books, because even honest people who sincerely intend to return them, often don't.
Rather than be annoyed with a friend, I've stopped loaning books, buying several copies when appropriate, just giving the books away, making it known that no return is expected. Costs a few dollars, saves a few friendships. And sometimes makes the friendship a little stronger, and triggers a reciprocal gift.