Draco wasn't stupid, he knew that this could easily go too far, but the way she melted under him, the wide-eyed way she trusted him, let him stop worrying about that. He also knew her well enough to know that if he did something she didn't like, she'd stop him - wouldn't she? If there was one thing in his life he felt like he couldn't actually fail at, it was being with her.
So when she kissed his jaw, he shivered and didn't try to stop himself pressing her back to the bed, following her mouth with his to catch it.