Sadly, cards get read once or twice, then forgotten. Would you like to give something that will be read again and again?
Use one of these beautiful books instead. Anytime your sweetheart does something nice for you, or you feel a rush of love and appreciation—write your feelings in this book. Then, leave it where he/she will find it.
Never tell when you’ve added an entry, let it be a surprise when your sweetheart periodically sneaks a peak at the book.