story identification - Teen soldier's brother is killed by the military, she goes on the run with the framed killer

There is a book I read once through, that had a sequel that I couldn't find at the time. In order to try to find the sequel now, I need to remember the title of the first book. Here's what I remember:

The genre is apocalyptic military, and the main character is in the military, and one day, her brother gets killed by a known enemy (who happens to be a very similar age AND a military prodigy as well) or so it's thought. However, from the boy's perspective, he didn't kill him, he was defending himself. So, angry and bitter, the girl goes after the boy, to hunt him down with intent to kill. So she finds the boy, but finds that he really isn't evil, and finds him very likeable, and no longer wants to kill him.

After they stick together for awhile, she asks him what happened that night and, come to find out, he didn't kill him, but did throw a knife toward him to stop him from following him (her brother was in the military and was trying to stop him after he stole medicine he needed) which, being the prodigy he was, accurately grazed his ear as intended, nowhere close to killing him. However, as he was getting away, he saw someone from the military murder him. So there is quite a conspiracy going on in the military.

Anyways, the military ordered the killing of her brother, which they don't know she knows. So, believing he is telling the truth, she starts hanging around him quite a bit, at which they start getting romantically involved (they're teens btw) the military discovers she's had plenty of time to kill him (or bring him in), but hasn't, and instead is just hanging out with him, considers her a traitor. So at this time, she goes on the run with the boy (whom was already on the run).

That's pretty much the summary of the first book, I just need to know what the title is so I can read the sequel.