The "Solitude" achievement can easily be missed.
There is only one opportunity to earn it. That opportunity comes when you initially enter the Tainted temple area to face the dragon, and he offers you a sadistic choice.
To get this achievement, you must accept the dragon's offer to sacrifice your beloved. Turn your back toward the dragon and walk away. Choose the associated responses when he asks if you are certain that is what you want to do.
This choice will initiate a brief cut scene followed by a roll of credits. When the credits stop, there is an option to retry.
No, you won't get to play the game as a Duke / Duchess. Your Arisen is simply shown seated (unhappily) on the Duke's throne, prior to the credits.
You'll gain the achievement, and (when you retry) return to facing the dragon.
Happy Gaming!
