Bloodline Revelations, Book 3, by Iuliana Foos

Theodora De Croix, the vampire Princess of the New Coven, endured the weight of the prophecy hanging over her head for five centuries.

Alex, the ancient alien she discovered in the desert, had learned their way of life, conquered her heart, and decided he could transform Earth in a new home for his people after performing one devastating procedure—cleansing.

She must pay for her eternal happiness with the existence of humanity, or, choose to save her world and live with a forever broken heart.