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Dean is so relieved that Sam's alive again that he bursts into tears. That sets Sam (and subsequently, Bobby) off too. "I missed you, Kiddo."
Sam smiles at him. "I've missed you, too." He pushes away the memories of Hell that threaten to overtake him. He wants to enjoy his reunion with Dean.
"Are you hurt? Sit down." Dean's overprotective tendencies have kicked in, but that's okay.
"I'm fine ," Sam replies, but he sits down anyway. It's better to listen to Dean.
All that matters is that Sam and Dean are together. Nothing will ever come between them again.