I loved this episode as well. All sorts of good character/relationship stuff. Everyone's really grown so much in the last couple of seasons.

My theory is that Charlie's forgotten they aren't married already :)

The absent minded professor strikes again :) I think he may think about it sometimes but then gets distracted by math stuff. Or I could totally by into your theory as well. I thought Amita asking "What's up with that?" was cute and showed how great her relationship with Alan actually is.