I cannot believe we don't have this one and Dear John article is about some show. Seen It A Million Times
Dear John We would never suspected this day would come. Even since we were separated from each other, our letters were only way we could stay in touch with each other. We were promising each other, that no matter what, despite our Feuding Families, despite you being called to the front, we will one day be together, either Happily Married or Together In Death. I was sending you letters, calling you „my dearest love”, „honey”, „my little bunny”, and so was you. As you see, this letter is different. I write to tell you, that everything that was between us is over. We're done. I cannot stand life in separation anymore. I found someone else. I don't love you anymore. There are plenty of reasons. Don't grief, neither was you first or the last who got such letter. Tradition of sending soldiers such letters dates back to World War Two or even World War One, which would make it Older Than Television. Good bye, my former love. You will never see me again.
Examples:Anime & Manga: