Dean was never one to care about a dude. But that all changed when he was pulled from hell by the angel, Castiel. A little while after hearing Cas say the words "Profound bond" in description of their relationship, he hung on to the words the angel spoke more tightly. What did profound bond even mean to Cas? Did it mean they were really tied to each other because Cas had saved him, or that they were emotionally, mentally, and forcefully bond?
It didn't even really matter to Dean, because for some reason, being bound to Cas in any way brought him pleasure. It was as though, even if he said he didn't have feelings for his friend, his jealousy was subdued by the thought that Cas couldn't really ever leave him. He could try, but maybe that profound bond would always make leaving him hard. Dean told himself that was bad, but really... he found it to be quite satisfying.