Postcard romance
So if we understood this correctly, this person who worked at a library actually indirectly met new people in his life years prior via a postcard. He found a postcard in a book, read it, and kept it, and then years later would meet the people who wrote it and begin a relationship with one.
Now if that is not a sign from the universe, we do not know what is then. That just has to be the best story ever for a setup of a romantic comedy. Someone needs to call a Hollywood producer to turn this little bit of information into a full-length film.