Snape is Good? What do you think about my theory?

Question:

Snape is Good? What do you think about my theory?

On JK Rowling's site, she talks about how the Order communicates with each other. She said they communicate with their patronus's. "The Patronus is an immensely efficient messenger for several reasons: it is an anti-Dark Arts device, which makes it highly resilient to interference from Dark wizards." When Tonks sent a message to Hagrid, Snape was able to receive it and know what they needed (the gates open to Hogwarts) If Snape were a dark wizard, he wouldn't have been able to get the message.
(SPOILER of Book 6)The only other evidence I can find is, breaking an unbreakable vow will kill you. We know he made one with Dumbledore to obey him. He also made one with Narcissa to kill Dubmledore. So the only way he can live is if Dumbledore ordered Snape to kill him.
I personally can't stand Snape, he is awful person. What are your thoughts?

Additional Details

5 days ago
"Members of the Order use their Patronuses to communicate with each other. They are the only wizards who know how to use their spirit guardians in this way and they have been taught to do so by Dumbledore (he invented this method of communication). The Patronus is an immensely efficient messenger for several reasons: it is an anti-Dark Arts device, which makes it highly resilient to interference from Dark wizards; it is not hindered by physical barriers; each Patronus is unique and distinctive, so that there is never any doubt which Order member has sent it; nobody else can conjure another person's Patronus, so there is no danger of false messages being passed between Order members; nothing conspicuous needs to be carried by the Order member to create a Patronus." Only the Order knows how to do it, and I think they would have noticed that Snape couldn't do one if he were a dark wizard.

Best Answer - Chosen by Asker: 5 days ago
"Members of the Order use their Patronuses to communicate with each other. They are the only wizards who know how to use their spirit guardians in this way and they have been taught to do so by Dumbledore (he invented this method of communication). The Patronus is an immensely efficient messenger for several reasons: it is an anti-Dark Arts device, which makes it highly resilient to interference from Dark wizards; it is not hindered by physical barriers; each Patronus is unique and distinctive, so that there is never any doubt which Order member has sent it; nobody else can conjure another person's Patronus, so there is no danger of false messages being passed between Order members; nothing conspicuous needs to be carried by the Order member to create a Patronus." Only the Order knows how to do it, and I think they would have noticed that Snape couldn't do one if he were a dark wizard.