Peter smiles at her. He was sure that he would be able to commit to not making things weird before he made that promise. But now he was sure that things would be okay. As long as they were okay with Liz.

"You want me to put a sock on the door?" he asks. "That's our Do Not Disturb signal. Me and Alec's I mean."

And before Liz gets the wrong idea:

"It's just for privacy. So he doesn't interrupt us when we're talking."

He doesn't want her thinking that he's ready to do anything with her yet, because even though she says she's fine, he's not entirely convinced she is. And he doesn't want to fool around with her until he's positive.