Why didn't Quirrell tell Snape about Voldemort? [duplicate]

Question

We all know Snape was a double agent (Death Eater and working with Dumbledore), but in the Sorcerer's Stone, he had no idea that Voldemort had latched himself onto Quirrell. This is evidenced in that that Snape is suspicious about some of the actions that he linked to Quirrell, and also confronts him about. But in the scenes that we see them talking privately, they never talk about Death Eater stuff.

I have not read the books and maybe there are talks of it in there, somewhere. But I think it would ruin the whole 'Snape is actually a good guy' plot line, so is that the only reason Voldemort did not expose himself to Snape?

Snape was also one of Voldemort's 'trusted' followers, because he let him get the teaching job at Hogwarts to spy on Voldemort (according to my sources).

It just did not make sense to me after looking a little into the Harry Potter series and re-watching the movies and this was the first thing that struck me as odd.

Why didn't Quirrell tell Snape about Voldemort?

Answer 1

The scene in The Half-Blood Prince in which Bellatrix and Narcissa turn up at Snape's house and he "reveals himself to be a Death Eater" and makes the Unbreakable Vow is greatly expanded in the books.

In it, Snape gives us the explanation for Voldemort's (who was controlling Quirrell at the time of course) lack of trust:

'I think you next wanted to know,' he pressed on, a little more loudly, for Bellatrix showed every sign of interrupting, 'why I stood between the Dark Lord and the Philosopher's Stone. That is easily answered. He did not know whether he could trust me. He thought, like you, that I had turned from faithful Death Eater to Dumbledore's stooge. He was in a pitiable condition, very weak, sharing the body of a mediocre wizard. He did not dare reveal himself to a former ally if that ally might turn him over to Dumbledore or the Ministry.'

Harry Potter and the Half-Blood Prince - p.33 - Bloomsbury - Chapter 2, Spinner's End

Answer 2

At that point, the Dark Lord likely doubted Snape’s loyalty.

It’s unlikely that the Dark Lord would have allowed Quirrell to seek out anyone who he had doubts about the true loyalty of. Before his resurrection, at least, the Dark Lord certainly seemed to doubt Snape was loyal to him. We don’t have any information about what the Dark Lord was thinking at the time he tried to steal the Sorcerer’s Stone, but we do find out he’s doubting Snape when he’s returned to a body.

“And here we have six missing Death Eaters… three dead in my service. One, too cowardly to return… he will pay. One, who I believe has left me forever… he will be killed, of course… and one, who remains my most faithful servant, and who has already reentered my service."
_{^{- Harry Potter and the Goblet of Fire, Chapter 33 (The Death Eaters)}}

The three living and absent Death Eaters are, in order, Karkaroff (the cowardly one), Snape (the one who’s probably left him forever) and Barty Crouch Jr. (the one who’s already returned to his service).

If the Dark Lord had any doubt at all who Snape would be truly loyal to, he’d likely not allow Quirrell to approach him. He was trying to keep his continued existence and plan to return to power as secret as possible - it’s unlikely he’d allow Quirrell to approach Snape even if he wanted to.

Also, Quirrell might not know Snape worked for the Dark Lord.

The Dark Lord found Quirrell in a forest in Albania as a lucky chance - before that, Quirrell was simply a teacher with no connections to the Dark Lord. As such, he might not know that Snape was once a Death Eater, as this didn’t seem to be common knowledge to most of the wizarding world. Without inside knowledge, he mightn’t even have considered the possibility of approaching Snape for help. However, more important is the Dark Lord’s desire for secrecy - Quirrell couldn’t do it without approval.