Dear Castiel,
I suppose we can appreciate the finer qualities of our first lovers spat. You have to forgive me if I seemed insensitive to the ways that you go out of your way for those demons in denim.
I can see how their taunts at the idea of freedom might appeal to someone as brilliant as yourself, but keep in mind how enjoyable complete and utter subservience can be. I am sure you will see it with you own eyes once our contract is finalized and you are forced to marry me. Not that it will be such a terrible thing. None of my demons yearn for free will over servitude.
Now it might do well for us to discuss your dislike of my tactics. You might think it distasteful to torture creatures of purgatory for information. Please consider the benefits and how they will outweigh your moral hurdles. If you actually tried torture you would find that it can be quite enjoyable.
I am not sure how Eve put together my plans of harvesting souls for your angelic war machine. Dreadful, how she confessed all that to the Winchester's along with the realization of my still being alive. Not that secrecy was a clause of our agreement, mind you. Still, I have to admit, when your cronies did her in, and you blasted the room in that astounding holy light, it took my breath away.
They could never comprehend how breathtaking you are. How your power only is second to my own. It is a shame really, to waste yourself on helping those fools when you and I can create such greatness together.
Dear sweet Castiel, together we could rule the world. Then, I would always be there to clean up your messes.
Thinking of you,
Crowley