What will happen to a man who receives such a breakup message?

Now it's good for you that you want him back. You don't really want to break up with him. You still have the luck to think that if you send this to him, he will treat you as before, right? If you really love him and he doesn't reply or just say something perfunctory after seeing it, then don't give him anything. If he really knows that he has done something wrong, forgive him.