Because I remain optimistic about this relationship, probably to the point of delusion, considering how things are going.
Dear Belle,
I know you are going to hate me for this. But lying to you always just makes things worse, so here is the truth.
Last night, after I told you to go see the world, I decided that I had nothing to lose. You didn't want me, even when my heart was cleaned of darkness, and so I had officially lost everything that mattered to me. I was going to die soon, unless I could make something change. And as wrong as it was...I thought of the darkness again. It never left me except for when the Apprentice sucked it out, and it's helped me not to feel helpless or weak. So I wanted it back.
And then Miss Swan and Regina came for Excalibur, because Emma planned to sacrifice herself and get rid of the darkness forever, and I found an opportunity to get what I wanted. I poured a potion on the sword before giving it back to her, arranging things so that when the darkness went out of all the Dark Ones past and present, it would go back to the dagger. It would go back to me. And before you start thinking what I know you are, it's not just about power.
I knew that if Miss Swan sacrificed herself, her parents would be desperate to get her back. They would most likely figure out what happened, and come to me and force me to open a doorway to the Underworld. And this would be my chance to try to find Bae. And even though it was the pirate who ended up making the sacrifice, the same principle works.
I don't blame you if you don't believe me. I wouldn't believe me either.
Miss Swan threatened to tell you if I didn't help her find her pirate. But I decided that I would beat her to it. I'm sorry. And you probably won't believe that either. I deserve that, but you deserve the truth. Goodbye, Belle.
-Rumpelstiltskin