it took me four months

I just finished reading "Harry Potter and the Half-Blood Prince".

What's this gloomy ending?
It made me disappointed.

Is Dumbledore really gone? I don't believe it.
But there is already a whtie tomb.

Where has Snape and Draco gone?
I don't like Draco but I don't want to make Snape a bad wizard.
He turns out to be the Half-Blood Prince.
Is he really a killer?