Castiel hesitates a moment, but ultimately takes the letters from Gabriel. Looks at them for a moment, the irrefutable truth that Gabriel didn't abandon him - not like Zachariah claimed, anyway. He's not sure how to respond to that. Were he more well adjusted, he might hug Gabriel. But he's not, he's been raised away from physical affection.

"It was my choice."

Half a statement, half a question. A statement - because he needs this to be choice, something he could decide on his own, something he could take for himself. And half a question, because he needs to believe that Gabriel didn't play him like Zachariah tried to play him.