Unless you never told them you love them in the first place, in that case that would be cruel because if they loved you back they would live the rest of their lives knowing that you'd loved them all along and that they hadn't taken a chance and told you, therefore they would live the rest of their lives thinking "What if...?"
This then lead me to the conclusion that this page didn't actually make that much sense and therefore you should not use your last breath to tell someone you love them unless you really really really want to.
There was also another page that I thought was silly it was called "If You truly Love someone Like this Page." I mean seriously? If you "Truly loved" someone you would be out there telling them that not liking a stupid page on a social networking site.