Afterglow Rising from the Ashes (Afterglow #1) by Stacey LP:
 
They came without warning, darkening our skies. For months, we fought to survive as everything we knew and loved was torn away. Then, as abruptly as they arrived, they vanished. Though the invaders left, the war wasn’t over yet. New terrors emerged from the destruction, threatening all that remained.

Alina could never have predicted the post-apocalyptic nightmare she woke up to. Foggy memories and the question of what had happened to her in the months she lost paled in comparison to the fear of the unknown surrounding her. But at least she wasn’t completely alone.

When she and her companion cross a camp of survivors, their world turns upside down in more ways than one.

Carter braved the invasion from the beginning. After tragedy struck, he was left questioning his purpose— in life, in love, in friendship. He fought for his group to survive, tirelessly pushing to reclaim what pieces of hope remained. And now, he will do anything to keep them safe.

In a world on the brink, alliances will be tested, love will be challenged, and the line between hope and despair will blur. Will they rise above the ashes and forge a new beginning? Or will they be reclaimed by the flames in the afterglow?