The Post Box {Lily/Severus Fanfiction}

One day, before Lily and Sev go off to Hogwarts, they find a Muggle post box which hasn't been used in years. They use it to communicate, before they go to Hogwarts. But this is where they tell each other everything, where they pour their hearts into each other. This is their place. Will it be forgotten over the years? Will they stop sending letters? Is it possible that this post box hides the deepest thoughts of two young children? Follow Lily and Severus through their Fourth Year, right until the very end.