If your character was that committed to being loyal to the slayers, he or she should have committed suicide immediately after meeting Talana and becoming tainted with dragon powers.
Personally, no matter how loyal I wish to be to a particular group, having them try to kill me kind of overrides that.
The point of the game is playing a dragon slayer who becomes a dragon knight. It would have been nice if Larian had the resources to add multiple quest solutions for main plot quests, so you could find a non-violent way to deal with the slayers. If you read the slayer's handbook, though, they are not exactly inclined to be forgiving or understanding (almost completing their intended genocide for the actions of a single dragon knight, etc).
