Showing Harry the stars at this point would probably kill him. The image of the stars is a talisman to him, representing the necessary triumph of human will over death. Harry has just made a resolution to unmake death, and we know he can do it because of Trelawney's prophecy. The next time he sees that image he is going to act on his resolution if he hasn't already, and right now he's exhausted and confused and desperately unhappy... He needs to be rested.

And besides, given that Quirrell thinks that Harry will destroy the world when he acts on his resolution, he should be diverting Harry's attention from the stars at all costs, and trying to bind him more strongly to the Earth and the people on it, which he is doing. I'm loving the irony of Voldemort desperately trying to remind Harry of all the people who love him.

Mind you, whilst I think Quirrell is smart enough to not show Harry the stars given what he knows, I could be wrong. So maybe he will try that at some point and it will blow up in his face.

EDIT: Hmm, prediction failed. I guess this means that I'm more swayed by emotion than Harry. No surprises there.