Even if you know what's going to happen, even if you know that they die, or have their heart broken, or damaged beyond repair, sometimes all you can do is hope. And hope just makes it all the more painful when you never see them again.
Cedric Diggory only ever wanted to make sure that the people he cared about were proud of him. He didn't hurt anyone. He was kind and considerate of others. He worked hard and devoted all his energy to achieving his goals. He was going places and his hard work had earned him a bright future. One that he could have used to change the discarding world for the better if he only had time. But Cedric, who was so happy to be chosen, so happy to be given a chance to prove that Hufflepuffs could be the best at something for once...He never got the chance to make his dreams a reality.
And Harry knew that whatever might have been, whatever the future could have held, couldn't change fact that he was looking down at a cold, glassy smile that looked nothing like Cedric Diggory and yet was. He remembered the look on Cedric's face when he was chosen. How Harry almost fooled himself over and over again into thinking that Cedric was looking at him when he smiled.
Cedric would never see the proud look on his father's face when he achieved his goals. He'd never change what he wanted to. He would just lay in the ground with that cold smile on that face.
Harry had dared to hope. Hope that they'd win the tournament together, and then maybe...maybe it could be different. But he watched as the coffin hit the dirt with a thud and slowly disappeared, he knew that hope had been the only thing left.