Who is Snape loyal to? *SPOILER WARNING*

*Spoiler Warning HP 7 & 6*

When I read the chapter where Snape kills Dumbledore, I first believed he betrayed him but then when I read it again I found that I was wrong.

I think Snape killed Dumbledore because he was in a position where he had to do it.

Why? Here's why:

-Dumbledore was desperate to get to Snape. He knew the only way he could have survived the situation was by getting to Snape before Draco or the other DE's found him. Why? Because...

-Dumbledore knew Draco had been enlisted by Voldemort to kill him, therefore I think it was Dumbledore who instructed Snape to offer to make the Unbreakable Vow to give Draco some protection as well as strengthing his position among the Death Eaters.

-Dumbledore was very calm when faced with Draco and the other DE's, and only started to plead when he saw Snape. He was pleading for Snape to kill him because he knew Draco couldn't bring himself to do it. DD was preventing Voldemorts backlash at Draco and his family (whom we can assume Voldy would have murdered as he threatened)and also prevented Snapes death because of the Unbreakable Vow.

By doing all this he ensured Snapes would remain in an excellent position amongst the DEs and would help Harry defeat Voldemort by backstabbing LV.

Do you think Snape is a traitor to Dumbledore or to Voldemort?