I wrote this back in 2007, right after reading DH. I haven't read that book in a long time and I haven't seen the movie yet, so I forgot how much of this is canon.
Quietly, Harry picked up a small rock and forcefully threw it into the black lake, wondering how it could all be over so sudden. While watching the rock peacefully sink to the bottom of the dark waters, his thoughts started to consume him, once again.
He had wanted to be alone for a while. Surely there would be people wondering where he was, why he wasn't celebrating with them, but he didn't care. He had just wanted to get away from all the people and the cheerful atmosphere, just for now.
Emotions were battling inside of him. Sadness and happiness and shock and fear and emptiness, and all he could do was hope that it would all pass as soon as everything had gone back to normal. But then again, when had his life ever been normal? His goal of the past seven years had been to defeat Voldemort, and now that that was done, it was almost as if he'd need to rediscover his identity. He supposed Hermione and Ron were going to get married, because honestly, everyone had seen it coming for such a long time that it was bound to happen within a matter of years. And he and Ginny were probably going to end up getting married as well, and they'd raise Teddy together and maybe have some kids of their own.
He wasn't quite sure how long he'd been standing there when he heard light footsteps approach him from behind. Turning around, he found himself face to face with the person he had least expected to show up at this moment: Draco Malfoy.
As neither of them wanted to be the first one to speak, it was Draco who hesitatingly broke the awkward silence. "Hey."
"Hey," Harry muttered back. He turned his back to the blond wizard again, facing the lake, hoping that Draco would take the hint. Apparently, he did.
"Listen, I understand you probably want to be left alone."
Harry nodded. "Kind of."
"But this is the last time I would be able to catch you alone, I figured. It won't take long, I promise."
Even though Harry wanted Draco to leave, he couldn't help feeling slightly curious. He turned around again, and sighed as he looked at the other boy. "Alright, Malfoy, say what you have to say."
"I…Well, you saved my life." He was struggling visibly. "Twice."
For a moment Harry thought he saw the cheeks of the pale Slytherin turn slightly pink, but he was sure he'd probably just imagined it. "I know," he said in a cold voice. "I was there."
Draco bit his lip. Harry almost felt sorry for giving him such a hard time. "I just…I just thought it would be appropriate to thank you. So…thank you."
"You're welcome," Harry said. He started walking, reckoning Draco wouldn't bother to follow him if he'd walk in the wrong direction, even further from the castle. He was wrong.
"Wait!" Draco called behind him. Reluctantly, Harry stopped walking. "I just don't understand. I never, ever did anything for you in my life. Why…All I ever did was make fun of you and your friends, and even worse, I'm from a Death Eater's family, I wasn't even on your side in this war! Why in the world would you bother to save my life?"
Impatiently, Harry turned to look up into Draco's grey eyes. "It's called humanity, Malfoy, something you'll probably never –" But his sentence was cut off, much to his shock, by Draco's lips covering his.
It was just a brief kiss, but by far the softest and gentlest Harry had ever experienced, and when he pulled away, he definitely wasn't imagining the pink blush on Draco's cheeks. He remained speechless for a few seconds, and then all he could manage was: "What…what was that for?"
Draco shrugged. "I don't know. To say thank you, I guess."
Harry felt himself getting angry. "And now, Malfoy?" Harry snapped, while trying to deny to himself how the stupid kiss had made him feel more alive with emotion than any kiss with Ginny ever had. He wasn't sure whether those emotions were good or bad, but at least he was feeling alive again, which was the one thing he needed right now. "What do you want from me?"
"I…I'm not sure," Draco replied weakly. "All this time, I've been such a…If I could, I would…"
"What, make it up to me? Did you honestly expect me to forgive you here and now for everything that happened between us in the past seven years, Malfoy? Because of one silly kiss? That's a little late now, isn't it?"
Draco lowered his head. "You're right, it was a bad idea."
Harry's expression softened when he realized Draco was being genuine. "You really hoped I…?" But the rest of the sentence faded away, as they both understood what he was trying to say. "I've got Ginny. And I love her."
"I know. I…I'll just leave."
Harry nodded in silence. But as Draco walked away from him, Harry couldn't help himself. "Malfoy!" He shouted.
When he saw the boy's desperate and somewhat reddened eyes look at him, Harry suddenly felt truly sorry for him, and said, "If things had been different...If...When we were younger..." his voice cracked slightly. "Things might have turned out differently."
"I know, but it's a little late now, isn't it?" With those words, Draco left, and Harry stared after him, until he was only a tiny dot in the distance that eventually disappeared into the castle.