Good questions, all of them. And I shall answer them openly.
This cycle, since about 1955. You see why I'm starting to be quite worried by all of this.
Both, neither, sometimes its a slow decline, sometimes its just as easy as a random stray thought that frees him. And sometimes, I suppose. It is the blood.
In my world it seems similar to any other, bite, a transfer of blood, you die, you don't stay dead.
As to what it means, do you want the spiel of the Old Ones or the real story. It makes you a monster. The older you get the more powerful you become but you are always, always a slave to the blood. We don't need it to surrvive but it calls to us. Its everything to us. An addiction one can never recover from.
Combine that with another me, one more vicious every time he's let free and you have your answer