Dearest Lily,
Why? Why did this have to happen? Please, please believe me – I never ever meant it to. You should know I would never do anything to hurt you. I'd do anything to bring you back, anything at all. I wish I could just die right now and be with you, but I can't do it. I'm too much of a coward. I always have been. Afraid to tell you how I felt about you. Afraid to lie about that god-forsaken prophecy – how I wish I had never heard it, that someone would have killed me before I could breathe a single word of it to him. I wish I could have been the one to stand in front of you, my life before yours. Because I would, Lily. In a heartbeat.
The only reason I'm still here now is because I know my death can't change anything. I know it won't – it won't bring you back. And I have sworn to Dumbledore to protect your son – your son still lives, the only part of you left that's not part of me, engraved in my memory. But I can't bear to look at him. He has your eyes, Lily, exactly your eyes. The most beautiful eyes I will ever see on this earth – but they look so jarringly wrong in the arrogant face of his father, every glance wrenches my heart. How unfair that so much remains of useless James Potter and so little of you. Why must it be so?
I'm sorry, Lily. I'm sorry for upsetting you so much when you chose him over me. The only reason is because I knew he could never love you as much as I do, as much as you deserve to be loved. Nobody could.
I'm sorry for everything, Lily. So, so sorry. I see now that I've done nothing but cause you pain. So many mistakes. Every day, every minute, every second, I wish that I could start over again. That maybe this time I could do some good in the world. If I could just make you smile, make you laugh, hear your beautiful voice once more, I know that my life would be complete. But I can't. And that's the truth – I don't deserve you, Lily. I never did. You were always too good for this world.
I only hope that someday you can forgive me. Because I know I can never forgive myself, for as long as I live.
I'm sorry. Please believe me. I know it can never be enough, but it's all I can say.
All my love, always.
Severus.