It is love all around, in the message and in the time spent making it... so here's a little tutorial if you are interested in making one yourself.
Step 1: Cut and fold the paper to the desired size to make the card. Note that using thin cardboard works great.
Step 2: With pencil and ruler, lightly mark a grid on the front side of the card. I made my squares one centimetre apart.
Step 3: With a needle make a little hole in each of the corners of the squares. If you know your design, think of it first and only make holes in the squares you will use for your cross stitch. That way your card will look neater. You will see in the picture that I marked the squares I was using.
Step 4: Erase the pencil marks. Thread the needle with yarn, in mi case I used red for the heart. and start stitching the crosses. I didn't make a knot in the back but left a little "tail" that then I could hide in the stitches.