The only thing I can imagine that's more selfish than trying to stop the wedding of a woman whom you "expected" to "follow" you when you moved across the country (but didn't), is inserting oneself into that emotionally manipulative clusterfuck by volunteering to write a love letter for the entitled young man because you're fucking bored.
You know, life isn't a romantic comedy movie. If a woman didn't follow a man across the country to be with him, there was probably a damn good reason. And if she got engaged to someone else, there was probably a damn good reason for that, too. And if the man doesn't have any clue if the woman will be happy to see him, that's a pretty good indicator that she probably won't be, even if he is bearing a love letter waxing rhapsodic about their future kids (!) that a stranger wrote but he totes copied into his own handwriting.