I sent a friend request to someone ages ago. When I checked his profile a few days later, the 'Add Friend' button was gone. However, it's now been ages and I checked his profile again and it has appeared again.
I am guessing the button was gone because he refused my request. Does the button appearing again mean that person has unblocked me or something? Or is it something done automatically by Facebook? Also, if it's the latter, does anyone know the exact length of time needed for the button to reappear?