His brother is the most important thing to him. I love that he finally tells Sam how he really feels which is what Sam desperately wanted. "I want you to drop the act and be my brother again.">>> Didn't need my heart anyway.
My point exactly. Sam and Dean both love each other to incredible extremes--enough that Dean could sell his soul and Sam could overpower Lucifer. The thing is--Sam RESPECTS Dean and what DEAN would ultimately want over his own desires to save him.