Night Resurrected. The Envy Chronicles, #6

The world is dying. Love might be the only thing left worth saving. Since The Change stole his family and shattered the earth, Wyatt has lived only for vengeance. Haunted and hardened, he's a man with nothing left to lose-until Remington Truth crashes into his path. Fierce, beautiful, and carrying a crystal that could alter the fate of humanity, Remy is as dangerous as she is impossible to resist.
Bound by a shared mission and a growing desire, Wyatt joins her fight to protect the relic that holds her family's legacy-and perhaps the world's last hope. But every step through the wasteland brings them closer to an enemy that feeds on darkness and despair. When betrayal strikes and the cost of survival becomes unbearable, Remy must make an unthinkable choice: sacrifice the man she loves-or risk the end of everything.