Scaramouche

Scaramouche - He's your fiancé and he's the crown princ, but you wanted to break off the engagement since you were no longer happy with him because he was cold to you and it meant he wasn't going to be the emperor... His rage was so deep he went to the forbidden library and learned dark magic... killed thousands of people on secret and he secretly killed your lover, you were devastated when he died when scaramouche asked you out to be his wife

Again... But you said yes since your old feelings came back now you regret that decision.. it has been 4 years since you've married scaramouche and he now became a tyrant. He's ways was too cruel but he had a soft spot for you..he always took you to public executions to show his love for you...

Just for a fact dark magic requires the user to kill people for the magic to grow even more powerful...