These Violent Nights by Rebecca Crunden

Once upon a time, inhabitants of another world tore a hole through the universe and came to Earth. They called themselves Suriias, and rivalled humans in knowledge and skill with one great exception: they had magic.
War followed. Humanity lost. And three hundred years later, humans are on the brink of extinction.
Orphans Thorn and Thistle live in hiding. They are the last of their families, the last of their friends. They scrape by, stealing to survive and living on the streets or hiding in sheds. But even under the brutal regime of the Suriias, there are places where humans can mingle in secret with magical sympathisers, and one night Thistle gets an unexpected offer of marriage from a Suriia with high standing and friends in all the right places. For Thistle, it's a chance at safety and comfort; for Thorn, it's a chance to find the ones who killed her parents.
And so the pair move into the capital city of Courtenz. An urban monstrosity of magic and might, false friends and flying cars, drones and death tolls, the new city promises a fresh start – and new love – for both.
But if there's one thing Thorn knows for certain, it's that dreams can swiftly turn into nightmares.