Alone Together Hostiles (Alone Together #3) by SS Fitzgerald:
 
Kill. Breed. Evolve.
 
The infected have a cycle—and it’s changing everything.
 
Three months after Captain Dillion Hawkins and Roland Donovan secured the survivors in Tallahassee, the rules of survival are shifting. It was hard enough when the infected only wanted to tear you apart. Now they’re adapting—and with every mutation, the line between humanity and monstrosity grows thinner. But the sane are just as dangerous.
 
A radical change on the planet is fanning the flames of fanaticism. Survivors are fleeing and falling victim to the fanatical demands. Survivors are being forced to choose sides, and whispers of rebellion are echoing through the ranks. With winter closing in and threats pressing from all directions, Dillion and Roland face impossible choices.
 
Which battles are worth fighting—and which lives are worth the cost? In a world that refuses to stop evolving, survival may no longer be enough.