Journey's End gone Wibbly-Chapter 5, What appears to be a solution
Jack slipped into the corridor Donna had disappeared into, and followed what appeared to be sniffling to her room, to where she had many suitcases laid out on her bed, and was desperately throwing clothes and toiletries into them, as though it would make all her troubles go away.
"Donna?" Jack asked, standing in the doorway, watching the pitiful scene. Donna's head snapped up, and quickly tried to brush her tears away. She gave him a watery smile, and asked him,
"What's up?" barely managing to remain composed. Jack smiled at her kindly and walked over to her, wrapping his arms around her. Almost on cue, she broke down in tears, pressing her face into his chest.
"What's wrong?" he murmured into her hair.
"The Doctor has Rose back. He doesn't need me. He doesn't want me. I'm leaving. I'm getting out, otherwise there's just going to be a whole world of hurt."
"Donna," Jack groaned kindly. "Of course the Doctor wants you! He's not like that! He's just happy to have her back!" He pressed his cheek against the top of her head, and sighed. "But you really don't want to throw this away! You might think you've got something amazing back home or a good enough reason to leave, but nothing compares to this. Ask me, or ask Martha, as much as you don't want to believe it, it's true." She brought her head away from his chest, and smiled up at him.
"What's your reason to stay on earth?" she asked. As soon as she said this, he smiled proudly.
"You wouldn't believe me if I told you." He said, his proud smile lessening slightly.
"Well show me then." Donna said softly, looking into his eyes. Jack's smile which was erupting inside of him was barely masked as one of sadness.
"If you leave the Doctor, when you come back…. It's like he's laughing at you. It's like he's looking at you, and his face is telling you that no one can function without him. I don't think he means to, but it hurts. Shit it hurts." He paused and looked at her sadly. "Unless you really think you are able to take that, your move back to earth… well, it would be permanent."
"So," Donna said stubbornly. "Show me why, and I'll stay. Show me forever." One second Jack was staring into her face, and the next, their lips met, their bodies pressed close together in a passionate embrace, and Jack finally felt that somehow, he just felt… right.