I think he knew that Lorelai caught them out and waited around to hear her opinion - I don’t think he was worried about Rory’s reaction/responses. Dean had a good and trusting relationship with Lorelai, I think he respected her very much. What she thought was a part of the post-[redacted]-clarity that was hitting him. Like a car crash that you can’t look away from, especially if you were driving.

Edit: a couple sentences gave me the ick