Well, if he doesn't talk to Narcissa, Harry probably still won't know he knows, because Narcissa doesn't yet know Draco knows.

And thank you! I know what you mean about over-the-top angst; there are some stories I've just given up on because the character barely has time to recover from one trauma- blindness, maybe- before the author also piles on brain damage and repressed memories and betrayal by his friends, and all sense of psychological reality is lost.

Draco is going to get more and more frustrated as he realizes how little information is truly available on Harry.

Harry's secrecy about the Pensieve is even worse, I think. If he decides to use it, no one knows it exists and so no one will be looking to stop him from using it.