If it was getting harder and harder for her to ignore his existance, then he was doing a good job. There was something about her that made Robert like her more and more each time they met, and he knew she felt the same, whether she was in denial or not -- otherwise she wouldn't have let him kiss her those few times and would've called the cops or kick his balls or something.
He chuckled at the sister comment. "I'd make sure you didn't have nightmares. And if you did, I'd wake you up so Freddy wouldn't kill you," he replied, smiling at her.