After leaving the washroom, Malfoy walked toward the Transfiguration classroom with his head lowered and a troubled look on his face.
When he first told Harry everything, he had felt a sense of relief, but it had soon been replaced by guilt.
He felt he had betrayed his father, yet he also felt he had done nothing wrong.
This was not the first time he had eavesdropped on his parents' conversations. Although Malfoy did not know exactly what had happened back then, he could always hear a sense of helplessness and forced compromise in their exchanges.
That thought grew like a weed in Malfoy's mind. He felt that if he could stop Voldemort from returning, perhaps he could free his father.
Of course, aside from that, the main reason Malfoy had given Harry the information was Hogwarts.
He loved the school, even if his deeply ingrained pure-blood beliefs meant he could never understand why it admitted those Mudbloods.
But that did not diminish his love for Hogwarts, so he did not want to see anyone destroy the castle, even if that person was his father or his godfather.
Yes, Malfoy knew Snape was involved too, but he had not told Harry. He felt that once Harry knew, if he successfully stopped Voldemort's resurrection, he would certainly not let Snape off.
Malfoy did not want anything to happen to Hogwarts, nor did he want anything to happen to his father or godfather. What he did not know was that Harry had even more information.
Not only Snape and Lucius, but even Jacob and those foreigners had already been exposed to the Golden Trio. Previously, however, Harry had only suspected that Voldemort's resurrection would involve the Diary. He had been unable to confirm it, but now Malfoy had done that for him.