Neville does what he can for her.
The first time it happened, he'd had absolutely no control of the situation. He certainly didn't mean for it to happen, and he didn't think she did, either. He wasn't sure what had possessed her to suddenly kiss his neck like that. They'd just been talking.
But before he knew it, his sweater was being pulled over his head, and she was crawling into his lap. He tried to protest, but it died in his throat as her lips met his.
He tried not to think about the way she was straddling him, tried not to look at her thighs as her skirt rode up too far. Instead, he stared at the ceiling, vaguely wondering if he was dreaming. But it was rather hard to ignore her when she began showering kisses on his face, loosening his tie, slipping her hands beneath his shirt...
Neville gasped at the warmth of her hands against his stomach. Reason getting the better of him for a moment, he grabbed her elbows, trying to prevent her arms from moving further upward. Why was she doing this?
"Ginny, I don't think--"
His protest was cut off when she looked at him. She looked so vulnerable, like she might break at any moment. He hadn't seen her look like that since her second year. One look at her and all thoughts of protest were gone. He doubted he could have refused her anything. In his mind, he berated his selfishness. He knew she would feel guilty about it later, but he let her continue. She hadn't been happy in what seemed like ages, and he told himself that he'd do anything to see her smile again, even if it was for just a moment.
Neville released her arms, looking defeated, and she kissed him on the nose. Neville was hard-pressed not to notice how far her shirt was unbuttoned when she leaned forward, though he was somewhat distracted by the way she was rubbing against his groin. He grunted and she pulled back slightly, grinning at him.
He tried hard to memorize the pattern of freckles across her nose, in case he was never able to be this close to her again.
Then she began working at the buttons on his shirt. Neville didn't move; he wasn't sure what he should be doing. So he left his arms stiffly at his sides, deciding to let her do as she pleased. This didn't seem good enough for her, though. She took his hands and placed them at the small of her back, just under her untucked shirt. She rubbed against him, and his hands moved involuntarily lower, pulling her bottom against him.
Ginny looked slightly surprised. "Sorry," he muttered, pulling his hands away. Ginny shook her head and kissed him on the nose again, returning his hands to where they had been, only this time, they were under her skirt. Neville blushed furiously, thinking that his trousers were becoming much too tight.
She slid his shirt over his shoulders, and soon she was trailing kisses down his neck; she worked her way to his collarbone and down across his chest as her hands worked at his waistline, tossing aside his belt and unfastening his trousers. He thought of protesting again, but then she finished unbuttoning her shirt and shrugged it off. Neville couldn't find it in himself to breathe, much less form a coherent sentence.
From that point on, he found it difficult to think of anything but the way her skin felt against his, her hot breath on his ear, how good her hands felt when she touched him. He wasn't exactly sure how it happened, but soon they were both naked, and she was wrapping her legs around his waist, and he thought that surely he would never feel better than he did in this moment.
Later, when she finally came, her eyes were closed, and Neville didn't have to wonder why. He tried to ignore it, but it kept gnawing at the back of his mind, and he hated himself for being jealous.
To his surprise, Ginny didn't seem to regret what they'd done together. But she didn't talk about it, either. It was almost as if it hadn't happened, except for the fact that she sought him out on many nights after that one.
Sometimes, she had her eyes closed the whole time. Neville never said anything about it. He tried to pretend that she was just savoring the feeling, even though he knew it to be a lie. He never refused her; he didn't feel himself capable of it. He was weak, and he knew it. But he told himself that he was helping her, which made clearing his conscience a bit easier.
Neville wondered if it would stop when he came back, even though he knew the answer. And he hated himself for wishing that he never would.