Sam
Any parent would die for their child. For their child's happiness. Willingly, happily and without looking back.
And Dean? Dean has always taken care of you. Even recently, while you were an infant, he was - quite happily - willing to see to your every need.
The bond you have with your brother is one that has always been there, I'm sure. But your father's sacrifice wasn't just for you, it was for Dean as well. He figured you belonged together.
And now? You can try getting along with him. The past is... past.