We don't know for sure. We can only guess at his true causes. But when you talk to him, he first says that he can drink the master's blood, and only then adds that we can also just kill him. Doesn't that indicate his priorities? By the way, I strongly regret that I looked at the spoiler... I mean, you're talking about something that's not officially available.
I'm not sure what you mean by not officially available, it's in one of his dialogues?