"Who's Cedric? Your boyfriend?" Dudley snorts and goes to turn away. For a moment, Harry wants to kill him, to use Avada Kedavra with no thought to the consequences. For a moment red anger surges through him and he forgets about the killing curse and just wants to throttle his stupid cousin to death.
Because Dudley doesn't know what it's like. He doesn't know how it feels to have to think every day, dream every night, about how Cedric died. To feel that it was all your fault. Harry blames himself. It was he who suggested that they take the cup together. If he'd listened to Cedric, then both of them would be alive. Alive and laughing together. Maybe Cedric would have been a little bit jealous. Even a little angry at Harry for winning the cup. Or maybe he would have had even more respect for Harry, facing Voldemort and surviving. Whatever he felt, he wouldn't have been dead.
Harry knows that Cedric's gone. He's accepted it- how can he not, when he's had to relive the death every night and every day? But he still hopes, deep inside, hoping without hope, that Cedric (who doesn't…no, didn't…know where Harry lives) will suddenly show up on the doorstep of number 3, Privet Drive, looking for him.
He remembers going to tell Cedric about the dragons. He remembers that the older boy was lying in someone's lap, having his hair stroked. He remembers thinking 'how arrogant' but still respecting and admiring the Hufflepuff boy anyway. He remembers the small stab of jealousy he felt, and how at the time he didn't know what it meant.
There's so much he remembers. Anger- Cedric going to the Yule Ball with Cho. Thankfulness- Cedric's hint helping him work out the egg clue. Fear- Cedric being attacked by Krum. Comradeship- Cedric telling him to take the cup and then coming to hold it with him when Harry suggested a Hogwarts victory. Sorrow and pain- when that hideous whispered voice said 'Kill the spare' and that terrible flash of green light destroyed Cedric.
But most of all, Harry remembers love. There were sunny days- and cold, miserable ones- when he escaped from Ron and Hermione and strolled around the lake with Cedric. They never talked. Just walked, and let their silence speak for them.
One day, they stopped walking. They were half-way around the lake, shaded from the rest of the world by a few trees, and they stopped walking, and looked at each other. Harry remembers every second. Cedric looked at him. A look that made his insides melt.
'You wanted to go to the ball with Cho, didn't you?'
'Yes,' he'd answered, being honest.
'But I got there first.' Cedric stared at the ground, looking thoughtful. 'So you like her, then?'
'I…I used to think so.' Harry shivered. He moved closer to Cedric.
'And…is there anyone you like now?' Cedric looked quickly at him, then looked away, his cheeks staining red.
'I…' At the time, he'd thought about his feelings. The way he felt around Cedric. The way his heart had leapt when he'd seen Cedric with Cho and the way he'd been unsure about who it was he was jealous of.
'Are…do you…' Cedric's breathing was uneven, as though he was nervous; frightened, even. Harry looked up. Saw Cedric's face. Moved towards him and let their mouths mould together in a perfect, perfect kiss. Cedric's arms encircled him. Their bodies were pressed close. Cedric broke away from the kiss. 'Are you sure, Harry?' Harry had kissed him again, to say yes. Then, when it had ended, they'd smiled at one another and continued walking.
And now, standing in this alleyway, his putrid cousin has the nerve to mention Cedric. Cedric, who died. Cedric, who was a Champion, and a good person. Cedric, who could have been so wonderful. Cedric, who Harry loved.
"Who's Cedric? Your boyfriend?"
So Harry draws his wand out of his pocket and advances on stupid Dudley. He doesn't know what he'll do; as long as it makes his cousin shut up.
Because what Dudley says isn't true- Cedric's not Harry's boyfriend. Cedric's never had time to be Harry's boyfriend. Because Cedric, beautiful, lovely, perfect Cedric, is dead.