This is super cute. Punch holes in a deck of cards (which make take some work). You can either paint a square on the “back” of each card or glue a small piece of paper where you can write your love note. Next, get Loose-Leaf Rings (available at dollar stores or where office supplies are sold). Put them in through the hole punches and you are done!
Don’t feel like buying those rings? Use yarn, lace, or ribbon instead. Just make sure it’s tied loose enough that you can turn the pages.