Imagine the day it just hits Draco Malfoy so hard why he’s been so obsessed with Harry for this long. Imagine him sitting there, thinking of nothing in particular, enjoying that his life is quiet for once. He thought about going back to Hogwarts to graduate, but he was certain he wouldn’t be welcomed and in the end the cowardly part of him one. So he’s studying on his own, he needs to prove himself, to show that he regrets what he did, that he does have good things to put out in this world. So he’s studying, right, and there’s a flash of raven black hair somewhere in his peripheral vision and his heart just jumps and he’s halfway out of his chair before realizing that it’s not Harry.
Maybe he studies for a while before it dawns on him why he’s feeling a little sad.