After the Battle of the Department of Mysteries, Draco had no doubt in his mind that Potter was the Chosen One, no matter what the Daily Prophet blundered on about. And if Potter was the Chosen One, he knew the war would be soon upon them.
Draco used to find all of the nonsense about Potter quite annoying, until the Dark Lord returned- none of his classmates were aware of just how dangerous everything was becoming, how dangerous everything already was. In a way, he figured it was his duty to show them the reality of the war, to help them realize that no one can be trusted. In the end, it is always about survival.
Draco had been given a job to do this year. He spoke of it to no one, begged the assistance of no one. If he survived, it would be his own doing. He did not want to owe anyone anything, especially not his life. Not in times like these.
He knew that Potter was trying to find out what he was up to. Draco wondered if Hermione suspected him as well. He wondered if she could hear his heart pounding in his chest when she caught his eye. He wondered if she remembered their fourth year, as he did.
It had been over a year since Draco realized he had feelings for Hermione Granger, over a year since he realized that being with her would be impossible. In their fourth year, they shared a kiss that Draco came to treasure as one of his most secret and cherished memories. His feelings for her hadn't wavered since that night on the Quidditch pitch, when Potter had announced, clasped to Cedric Diggory's body, that the Dark Lord had returned.
All of these things Draco pondered in Potions, ignoring Slughorn's obnoxious praise of Potter's lilac liquid and staring at the witch who grew steadily more frustrated with her own deep indigo gloop. He fought to keep his chuckle contained as she hastily added more ingredients.
For a moment he even wondered if he had made the right decision in his fourth year. After all, he had only been 14 when he decided to sacrifice her, to join the cause his father was so proud of him for following. But the Dark Lord was more terrible than Draco had ever imagined.
He sighed at his cyclic thought process. By leaving her, he was letting her live. Keeping her, if not safe, at least alive. And so he went back to normal. Or rather, as normal as he could pretend to be around Hermione, while the Dark Lord breathed ominously (and metaphorically) down his neck.
Draco thought back on the Battle of the Department of Mysteries. That fateful night had both given Draco more freedom than he'd ever had, and snatched it away tenfold. Suddenly, with his father gone, no one could scold him for fraternizing with the enemy. Then the Dark Lord sank his teeth into Draco, gave him the ultimate death-sentence: Kill Albus Dumbledore.