Obsidian was written by Jennifer L. Armentrout.
Katys´ new neighbor Daemon is the worst. Sadly, his sister Dee is one of the nicest people Katy has ever met and they soon befriend each other much against the liking of Daemon. Katy has no idea why until she finds out that her neighbors are aliens and that she walked right into the middle of a conflict that was never meant to be seen by a human being.
I´ve read the first three books of the Lux series last year but tbh I kind of really hated the third one so I stopped reading it. But I´ve set myself the goal to give shit books a second chance so I went out and bought Lux Beginnings, the super ugly special collector´s edition, which includes Obsidian and Onyx, the first two books in the series and the ones I liked before I picked up the third one. I haven´t reread Onyx yet but I was not disappointed with Obsidian and I liked it as much as the first time I´ve read it.