Kate Bishop and Castiel
"I've known Balthazar for a long, long time," he said. "He wouldn't do anything if he knew I would be hurt by it. That's one reason he has tolerated the Winchesters here, I think." He shrugged a bit at this.
He did trust Balthazar immensely. He trusted the other angel with his life. He would do anything for him.
"Now I know what to feed you if I see you again and you're hungry." Pizza seemed to be a popular choice among humans, it seemed.