"I guess I just uh…I wish you were coming, that’s all."
"Don’t be stupid."
"No I mean it. You know plenty of good hunters. I’m rusty, and I did something seriously stupid going out there, I almost got us both killed."
"Well that’s exactly why I want ya."
"What are you talking about?"
"You just went, you didn’t hesitate. Because you care, because that’s who you are. Me, I wouldn’t even think to try."
"Yes you would."
"No Dean…I’m telling you, it’s just better with you around that’s all."
Season 6 Episode 1: Exile on Main St.
Dean has always kept Sam in check (or at least tried to), and vice versa. Soulless Sam knows that…he likes it better when Dean’s around, because he’s less liable to do something stupid and reckless (like we find out later he has done). They keep each other safe…but more importantly (as previously said) they keep each other human. Soulless Sam has all of Sam Sam’s memories…and he remembers that speech…he wants his brother around to be his conscience, his helper, his protector, his mentor…his brother. He’s been without him for a year, and he misses him…but he also misses how he is with him. He feels more human when Dean’s around.