The Doctor was not - could not be, in any form, daft. The Doctor with the human heart, a heart full of love for Rose, a heart that could actually be given, knew what had been done to his counterpart. He knew the pain that The Doctor was experiencing - the same pain that the human Doctor himself would have had to bear had things gone the other way.
But The Doctor's pain was not important. It was almost an unspoken agreement between the two Doctors. They both understood that it was a necessary agony to endure in order to give their beloved Rose Tyler what she truly needed. And The Doctor wanted nothing more in his life than to do right by Rose. Though, deep in his hearts, he wished that she would refuse their scheme to, once again, save her against her will. But his convictions were confirmed when he saw the pique in her interest when the human Doctor explained that he had only one heart, that he could grow old with her, and be hers forever.
And then she asked him to finish that sentence that he'd begun so long ago, and he wanted nothing more than to confess to her that he loved her with all his hearts. That he had loved her for years. That she was the most amazing woman in the entire universe, and he knew that for a fact. But he couldn't.
"Does it really need saying?" he asked. He'd allow Rose her happiness. He'd give her what she needed. And he knew that she'd be in good hands - his, though not his own.
He watched as the human Doctor leaned in to whisper what they'd both been dying to tell her from the moment they'd laid eyes on her, and then averted his gaze when Rose grabbed the human Doctor and kissed him. It was painful to witness, and the Doctor knew that if he didn't leave now, he never would. She would convince him to change his mind, somehow...And he knew that if she asked, he'd wouldn't be able to resist. No. He had to do what was best for her. He must give her what she needed. Because that's what love is. And he loved her. He loved her so much. And now, she'd get to hear it every day, the way she should. So, once again, The Doctor left Rose Tyler standing on the beach of Bad Wolf Bay.