Well if you keep working on it, you may just get a book deal and not have a reason to kill yourself... that would be ideal.
But lets get to the root of this problem, Why write the letter? Why not tell the person directly? Why not tell some one? Maybe they can change your mind, because a human voice is much better then a forum post.
I understand, I've written many of letters, threw'em all out. You wanna know why? Because that feeling, is temporary.
I don't know you, I can't give you much of any answer, but I can tell you that the letter will never be good enough, and will never be able to excuse your death. Maybe you shouldn't stop writing, write till it hurts, write till you can't write anymore. And then honestly look at yourself in the mirror and ask "Is this worth it?"
If you have the energy and desire to write a suicide note, why not summon that same energy to find a reason, any reason to live. Why end your life needlessly when it can be used. Yes a life can be used, you are a person, you have a will of your own, and when there is a will... my friend there is way.
If you really hate yourself that much to die, why not just use the body and mind you were blessed with to actually help people who want to live, you never know, you might just feel better about yourself in the end. I know I do.
Just PM if you ever wanna talk. I'm not being hard on you, I just want you to open your eyes.