Sam simply let Dean do the talking. He was curious to hear what Jennifer had to say, especially since that would hopefully point them in the right direction. He was a little irritated that this thing was so difficult to place.
He didn't care either way as to what Dean's relationship was to Jennifer or Dinah or anyone else, save for the fact that it at least seemed like Dean hadn't completely gone all Stepford on him so that was in the plus column he supposed.