They both die at the end / Adam Silvera.

When Mateo receives the dreaded call from Death-Cast, informing him that today will be his last, he doesn't know where to begin. Quiet and shy, Mateo is devastated at the thought of leaving behind his hospitalised father, and his best friend and her baby girl. But he knows that he has to make the most of this day, it's his last chance to get out there and make an impression. Rufus is busy beating up his ex-girlfriend's new boyfriend when he gets the call. Having lost his entire family, Rufus is no stranger to Death-Cast. Not that it makes it any easier. With bridges to mend, the police searching for him and the angry new boyfriend on his tail, it's time to run. Isolated and scared, the boys reach out to each other, and what follows is a day of living life to the full. Though neither of them had expected that this would involve falling in love.