I decided to write this after thinking:
What if, after Rosalie mistakenly told Edward that Bella was dead, he didn't go immediately to the Volturi? What if he first wrote a letter to Bella, telling her the truth about his absence and his real feelings for her? And what if Aro caved immediately and killed Edward as he wished; and all Bella was left with was the letter? Edward would be dead but he would still live on in Bella's heart.
Dear Bella,
I lied. I've always loved you, and I always will. I go now to Volterra to ask of Aro the thing you made me swear not to; but on this day I am prepared to die. I love you Isabella Marie Swan and if I cannot spend my life with you then I will not live it at all. How I will miss cradling you in my arms and humming your lullaby to whisk you away to sleep. The blush that crept up into your cheeks and the warmth you made me feel have brightened my world and made you my reason for living.
I didn't want to leave you. Please believe that. If I could have you right here to "dazzle" you, I would. I pigheadedly thought that I could protect you by leaving and that you would learn to love another. I knew I would never get over you, but the thought of a better, human, life for you kept me away. If I had been there… oh, Bella, I would give anything to have been there.
When I told you I didn't love you it was the biggest lie I've ever told. I've loved you since the moment I set eyes on you; your big brown eyes were pools of emotion that drowned me in passion. I know now Bella that you loved me. I have to ask… why did you believe me? I thought it would take hours of persuading for you to even acknowledge what I was saying. Alas, my darling, you believed me the minute I said it and for that I am forever regretful. You never have, seen yourself clearly, and you didn't then. You were more beautiful than anything else on this godforsaken planet and I was lucky to have had you the few short months I did.
How I wish I had turned you! Bella, you must understand that I truly did think that this was best for you. I could not bear to steal your soul away and make you a monster because that isn't you. You were an angel, and for awhile you were my angel. That is why, even though you are gone, I am content that you are in heaven watching me as I write this letter and make the decision to end my life.
I lied when I said I didn't love you. And now I break my promise.
If by some chance we do end up together in the afterlife, whole and unscathed then please forgive me. If not, then know that I love you and am forever yours. Wherever you may be, you will always hold a place in my heart.
Love always
Edward