"Cas," Sam asked rather bluntly one day. The other man turned curiously towards him. Once he had his attention, he continued. "So are you in love with Dean?"
"Um, no." Cas answered, but he was blushing, so...
"Then why do you always write 'C+D' in hearts everywhere?"
He had got him there! And to his credit, Cas really did pause. Then he answered.
"...it stands for cynical and damaged."
Well it wasn't like he was wrong. They'd been through a lot of things, after all.
Deep down, Sam knew the truth.