Pieces:

When his parents died, Dick wondered why God didn't take him too. Why did he survive and they didn't? The guilt was eating him alive, until he found the Batcave and became Robin. He found an outlet for his anger, the guilt, which was coursing through his veins, and for a while, Dick was okay with that. Even as a piece of his heart broke away and shattered, never to return.

When Tula died, the guilt that came with it wasn't as heavy as Dick remembered. It was dark, of course, but nothing like the all-consuming numbness that had plagued him when he first experienced a loved one's death for the first time. Maybe it's because he wasn't as close to her as he'd thought. Another piece, smaller than the first, was gone.

Then, Zatanna and Rocket left the Team to join the League, and took two pieces of his heart with them; two small, but just as important pieces with them.

Wally and Artemis left soon after, leaving him with Superboy, Miss Martian and Beastboy, who'd join a few days after Zatanna and Rocket had left. Wally took a large chunk with him and Artemis, a small one. Dick felt like he was drowning, Robin continued to fight to stop the nightmares.

When Bruce fired him, Dick was left with just one quarter of his heart left, throbbing painfully in his chest. He needed something other than Robin to overcome this. Robin held too many memories already. Dick became Nightwing.

Jason died. And Nightwing grieved. The guilt was back, crushing him. This time, only three tiny pieces were left.

When Tim came, Dick felt like his heart may actually gain back some of those pieces he lost, and he did, until he had his heart back to a quarter. He's never felt as happy as when he was with his little brother. I will be okay, he thought, but sadly, good things never stay good and bad things always happen.

And then, Wally had to die. And the ginger had taken what was left of his heart with him, leaving Nightwing, an empty husk, behind. Of course, he would smile, he would laugh, he could put on a mask, but no one would ever see the bloody hole that was left in his chest.

And people wondered why Nightwing had chosen to fly solo. He just couldn't take the pain anymore.