There has been plenty of instances of long distance relationships which lasted for a long time before the two people actually met.
As early as the 1600s, colonial Quaker writer Elizabeth Ashbridge writes about a man in Massachusetts Colony writing letters to a woman in Ireland. They never met before and only corresponded because a friend introduced them to start writing. The relationship lasts for 10+ years while he remains in Massachusetts on the King's duty, and both of them stays chaste and faithful to each other.
IT EXISTS, and unfortunately, there are also predators out there that like to fuck with people.
There is a show called CATFISHING, and it is all about people online falling in love with someone who they thought was legit, but turned out to be just a prankster.