How comes Dean came back to save Sam in the pilot when Jess was on fire? I mean could he know smth. happened?

Check out this link! :) This scene is on the dvd under "deleted scenes". Dean's watch had stopped, and he knew something was wrong. Why they cut this part out is really a mystery!

link

because just knew and i think he want one last chance to ask sammy to go with him

because the radio in the car started cutting out. its a sign of a demon.

I always thought he'd stayed around a bit wanting to ask Sam to come hunting with him again, so he saw the light of the 火, 消防 from the window.