Once upon a time, he would've said the greatest pain he felt deep down in his heart was losing her. One word was all it took. One word did the work the years of drifting away could not accomplish. One word that was the dagger thrust in the gut slicing through the aorta.
One word.
To see her with another man was torment enough. To see her with his rival, though, that was the Cruciatus curse each and every time he saw them together.
Potter, with his friends. Actual friends who care about him and love him. Friends who did not need to be kept at an arm's length. Friends who could be told anything and everything…and they would not give the information away.
Potter, with his family who loved him. Potter, never having to deal with an abusive alcoholic father or a mother so beaten down that she could not take care of her own son.
Potter, the athletic one. Potter, who got away with every prank ever pulled. Potter, who saved his life because the alternative was to let one friend become a murderer and the other the cause of the murder.
This was the man she chose over him.
And now…the pain he once felt now feels like a softer, paler version of the pain residing in his soul. She is now gone, forever. Killed by a curse, the green of the curse matching the green of her eyes. In her place, her son lived. Her son, with her eyes. Her son, the living embodiment of his rival.
The pain stays, never ebbs fully away. It rushes back in when he dwells on the fact that he was the catalyst for her death. If he had never spied, never told, then the Dark Lord would never had known, and she would've been safe. Alive, with Potter and the brat, but safe.
The pain rushes back in when he sees her son in his class. And it continues to flow back to the forefront each and every time he sees the child. Six years, the child is in his class room. Six years of seeing her eyes, but Potter's face. Six years of fantasizing of punching Potter's face, but saving her eyes.
The seventh year is the reprieve. He does not see her eyes staring back at him in class or in the Great Hall. The year is dark, depressing, but at least Potter's face is no longer taunting him, even though he misses her eyes.
When he's confronted by the child, now a young adult, he falters. Her eyes, staring back at him. Her eyes, telling him he is a good man, even if the young man is shouting that he is the enemy, the bad guy. The pain intensifies.
The pain soon starts to ebb away for good, when the snake venom starts coursing through his veins, when the memories begin to spool into a silver ribbon.
With one last look into her eyes, the pain finally ends.