Strain — Amelia C. Gormley

Rhys Cooper is a dead man. Cut off from the world since childhood, he's finally exposed to the lethal virus that wiped out most of the human race. Now his only hope for survival is infection by another strain that might provide immunity. But it's sexually transmitted, and the degradation he feels at submitting to the entire squad of soldiers that rescued him eclipses any potential for pleasure -- except with Darius, the squadron's respected, capable leader.

Sergeant Darius Murrell has seen too much death and too little humanity. He's spent a decade putting plague victims out of their misery and escorting survivors to a safe haven he can never enjoy. He'd rather help Rhys live than put him down, so when Rhys can't reconcile himself to doing what's necessary to survive, Darius is forced to save Rhys in spite of himself.

But with each passing day, it looks less and less likely that Rhys can be saved. And that means that Darius might soon have to put a bullet in the head of the one person in years who reminds him of what it means to be human.