They both knew what Lawrence, Kansas meant, what happened there.
Dean told Sam by drinking an extra shot at the local bar, and Sam told Dean by kicking the motel door shut instead of making the extra trip.
They weren't in the talking mood.
Thank god,
They both understood that when the lights went out they both needed extra comfort and one less bed.
There was only one thing that would make this situation better:
A rather non-conventional chick flick moment.