Lily was the first to ask. At the time my greatest secret was little more than that I wore only second hand clothes, I hated my father, and my mother was a witch. I never had to tell because Lily was too curious for her own good and had me figured out before I could get the courage to tell her. It's too bad that I could not tell her the one secret that defines me and who I have become. I cannot tell her, because she already knew.
Albus was the second to ask me. I never did tell him you know. I lied instead and told him of my misguided foray into the dark arts and the world of death and destruction. Something else I am deeply ashamed about, but it comes nowhere close to my most guarded inner thoughts.
Voldemort was the third to inquire. "What is your deepest, most darkest secret Severus? I can make all your wishes come true you know. You have but to ask and I will give it to you for the taking." The vile man tried to pry the information from my mind, but there is no prying what cannot be found there. The information is embedded so deeply into my heart, that I know every fiber of my being reeks of it, but Voldemort never did prize away even the outer layers to see what hides inside.
My name is Severus Tobias Snape, and I have a secret that I don't know how to tell. I'm dying inside a little each day... it's my own private hell.