Reached

Reading a romantic fictional novel, what do you look for? A girl who's torn between two boys, along with her worry about the society she lives in, that they're not telling the truth. That's exactly what happens in the Reached trilogy. In the first book, Matched, Cassia is investigating the mystery surrounding Ky, an Aberration. Being an Aberration means he can never have a Match. Yet his face came up on Cassia's microcard she got for her real Match, Xander. After that, she unintentionally got Ky sent away to the Outlands. In Crossed, Cassia runs after Ky and escaped her camp and prison. She makes her way through many things, including the starvation pill she accidentally took, and a camp that is now empty. In Reached, Cassia helps overthrow the Society and work to create a new world. When Xander and Cassia pick up Ky, he finds out that he is not immune to the new Plague, but Cassia and Xander are. I think Ky's going to fall ill to this new cure and seem to become an extreme case. 

This prediction can be supported by the text in a couple of ways. First, when they are locked in the cargo hold for the ride back to the Rising base, Cassia and Xander tell Ky that even though they are immune to the mutated Plague, they could still be carriers. Being locked in a cargo hold for a couple of hours with almost no air circulation, Ky is sure to catch the new form of the Plague. And the risks run even higher with Xander, because he's been working around people with the sickness almost all the hours of his day. He has been exposed to different symptoms  of the Plague, and Ky is breathing the air with all of those sicknesses in it. 

The second reason is just because it makes sense for the author to make Ky fall ill. In a book, you need to have a tragedy, so to speak. Something to distract the main character from any thoughts he or she might have except for this event. When he does fall sick, Cassia will not be able to think of anyone else except Ky. 

This book is a lot like Mockingjay. In that book, Peeta, one of Katniss's love interests, is taken by the Capitol and brainwashed to think that Katniss is his enemy. Katniss can't think about anything else except Peeta, and she tries anything to get  him back. Sometimes it looks hopeless for her, but she pushes on. I think Cassia will do the same thing for Ky, and when the time comes, she'll choose him for her Match, and Xander will find someone else he cares about.

Cassia and Ky have been through too much together to not become a couple. Xander has been there for her, but Ky was the one who stole Cassia's heart. And after he recovers from his illness, Xander will see that and start trying to find someone else who will love him.