"You'll leave," came the muffled voice. "One day. You'll leave me for good."
Donna looked down at the Doctor, and pursed her lips sadly. Curled up in the grass with his head in her lap, an air of exhaustion dragging at every ounce of him, he made a sorry sight.
She moved her hand, resting on his shoulder, to gently run her fingers through his hair. "I won't, Spaceman," she said, not for the first time that day. "I swear."
He gave a short huff. She supposed it was meant to be skeptical, but he trembled with the effort, and there was no energy behind it. He'd been like that all day—been resisting it for much longer, she figured, ever since their talk at the UNIT base—just lying around wherever he found himself, trying and failing to sleep off his low mood. She'd barely been able to drag him out here, under a tree in the nice little meadow that had become a favourite picnic spot of theirs; she knew the fresh air and sunshine would help him soon enough, at least a bit, but he didn't seem to have gained any headway yet.
"Dunno why I bother with this," he muttered after a moment. "Dunno why you do, come to think of it."
"C'mon, don't talk like that," she chided gently. "I'm not bothering with anything, you prawn."
"You are," he said, and his tone was scathing. She flinched, knowing it was directed at himself. "And you shouldn't. Bloody waste of time."
"Hey." Leaning forward a bit, she looked at him sternly. He turned his head further into her lap. "It's not a waste of time. I'm serious, don't tell yourself that sort of thing."
"Why not?" he demanded, his voice wavering. "What does it matter? You–" He shut his mouth abruptly, shrinking back from whatever he'd tried to say. Then he sagged, letting himself go limp once more. "Never mind," he sighed.
"It's okay," she said gently. She brushed his hair back out of his face, and he closed his eyes. "It's okay, you can say it. What's on your mind, Spaceman?"
It took him a minute to work up the courage to speak; when he did, his voice brimmed with pain.
"You won't stay," he mumbled. "Here I am, getting used to– to having you around, having someone to drag me outside. Getting… attached." He said it like the concept both bewildered and terrified him, and he gave an incredulous laugh. "Stars, you would think I'd have learned better by now. You all leave, sooner or later, you all get bored of me eventually, I don't know what I expected. Heartbreakers, the lot of you."
Donna recognized his attempt at humour, but she could hear that he was on the verge of tears. Sorrow tightened like a vice around her throat.
"Oh, Donna," he whispered, almost inaudible over the soft sounds of rustling grass and birdsong. "I don't know what I'll do."
She was quiet for a moment, her hand stilling where she'd been playing with his hair. There was a reason, she knew, that he'd assumed she was leaving permanently; it was really no wonder he worried sometimes, what with all the people he'd lost in one way or another. No wonder he tried so hard to keep up his casual façade—no one could hurt him if they never got close. (In Donna's personal opinion, he was quite rubbish at it, but she sympathized with the attempt.) And if she could claim to understand anything about her daft Spaceman, it was that he didn't do well on his own. She'd known that from the start.
No wonder he was scared.
"You know," she began, picking her words carefully. "I mean it when I say I want to stay with you forever. Or as long as I can, at least. I– I'm not in it for the travelling, not really, I… care about you. You daft Martian. You're not a hobby, or a– a plaything, Doctor, I would never abandon you like that. And I…" She cleared her throat, surprised to find herself getting choked up. "I'll do everything in my power to stay with you. I promise you that."
The Doctor didn't respond, but went very still under her touch. He wasn't too tired to put his guard up as he considered her words, sifting through the sentiment and, doubtlessly, finding evidence to the contrary.
"I know you probably don't believe me," she said. "That's alright. But honest, you don't have to worry about me running off. I'm here 'till you kick me out. I'll prove it to you."
There was a long silence. Then he gave a shaky exhale, and mumbled, "Thanks."
"You got it, Spaceman," she murmured.
A soft smile tugged at the corners of his lips, then faded once more. His gaze went distant. Donna resumed stroking his hair gently, hoping to draw him out of his thoughts.
He hesitated. "I'm still tired," he said quietly.
A sympathetic ache started up in her chest. "I know." She reached for his hand, and he obliged, letting her hold it tight and rest both their hands against his chest. "I'm sorry, Spaceman."
The Doctor swallowed, and nodded.
"Stay here awhile," she suggested. "Get some rest, and we'll see how you feel later." Then she added, "I'm not going anywhere."
He sighed. "Yeah. S'pose." He shifted a bit, curling up a bit smaller and pulling her arm tighter around him. Donna couldn't help a little smile; he made a sorry sight, sure, but a terribly endearing one as well.
"I'm proud of you, you know," she said. She gave his hand a squeeze. "I know it's hard. I'm very proud of you."
He didn't respond. She didn't expect him to; the poor thing could only handle so much vulnerability in one go. But after a moment of consideration he squeezed her hand in return, rubbing it briefly with his thumb, and her smile grew wider. It was more than enough for her.