I'm the Villainess, So I'm Taming the Final Boss, Vol. 1 (manga)

Avoid the bad ending at all costs! When her fiancé breaks up with her in front of the entire student body, noblewoman Aileen d'Autriche is devastated-or she would have been, if that wasn't also the exact moment memories of her past life came crashing back! Turns out, she's been reborn as the villainess of a dating sim...and according to the story, she's slated to die at the hands of the demon king in three months! But Aileen's already got a plan: Step one, get Demon King Claude to fall in love with her. Step two, live!