I've always thought that it was entirely reasonable for Harry to fall for Ginny over the course of this summer, as Rowling writes. Here's a conversation which may have happened in that time.

Swoosh. Silhouetted against the darkening sky, Harry made one last sharp turn on his broom, before diving at high speed back towards the ground, stopping with less than a metre to go. As he walked back towards the Burrow, Ginny noted the way his cheeks were flushed and his eyes alight, even more so than they had been during their earlier pick-up game of quidditch. Harry froze, seeming to notice her suddenly. "What are you doing out here?" he asked sharply.

Ginny just looked at him tranquilly. "Oh, you know… Enjoying the night-time air." She gestured to the sky and smiled slightly. "You've still got it I see."

"Yeah…" Harry turned and headed indoors, the bounce in his step slightly reduced. As he reached the back door into the house, he turned back abruptly. His face was now slightly anguished. "By the way, I want you to know… I'm sorry," said Harry. "I should never have dragged you all to the Ministry."

Ginny frowned, not having realised he was still blaming himself for that. While she was processing this, Harry had turned to go inside. "Wait!" He turned back. "You realise we all chose to follow you, don't you?"

He nodded, his face still overclouded, as he leaned against the wall of the porch. "I still led you into danger. Sirius died because of me."

Ginny bit her lip, unsure how to respond, then began to up the tempo of her argument. "Sirius chose to be there too. Fighting Voldemort isn't just your job, you know?" She was now face to face with him, daring him to contradict her, and Harry was watching her closely. "It's part of all of our lives, whether you like it or not."

Harry seemed defeated for a moment, but then sighed. "Why don't you all hate me?"

Ginny rolled her eyes. "Why should we? We all know how much you love Sirius. Your loyalty to those you care about - your desire to protect us - is precisely why we chose to follow you." Ginny leaned deliberately against the wall, right by Harry. Through her top, she could almost feel his arm brushing against hers. "Look, every single person who went that night chose to be there. We don't need you to say sorry. And if anyone is to blame for his death, it's Bellatrix, or Voldemort. You didn't kill him."

Harry's face looked slightly lighter after this, as he appeared actually to be taking her argument on board. "In that case," he said thoughtfully, "I never said thank you, did I?"

"For what?" asked Ginny.

"Well…" A slight uncertainty flicked across his face. "For everything I guess."