He didn't want to answer the question. Much like his uncle, she didn't expect to ever get the full truth out of him. There was something that Draco wasn't telling her. Likely a lot of somethings. If she was wiser, she would run out of the flat and never return. But, as he'd had occasion to remind her of, she was too damn curious for her own good. If there was even the slightest hope that he might tell her what she wanted to hear, she wouldn't leave. He held a special power over her that she resented.