Shadow Kiss (Vampire Academy #3) by Richelle Mead

It's springtime at St. Vladimir's Academy, and Rose Hathaway is this close to graduation. Since making her first Strigoi kills, Rose hasn't been feeling quite right. She's having dark thoughts, behaving erratically, and worst of all... might be seeing ghosts.

As Rose questions her sanity, new complications arise. Lissa has begun experimenting with her magic once more, their enemy Victor Dashkov might be set free, and Rose's forbidden relationship with Dimitri is starting to heat up again. But when a deadly threat no one saw coming changes their entire world, Rose must put her own life on the line - and choose between the two people she loves most.

“You will lose what you value most, so treasure it while you can.” 

“And I thought the whole point of my education was that violence IS the answer.”

“You aren't afraid of throwing yourself in the path of danger, but you're terrified of letting anyone in.” 

“Throughout history, people with new ideas - who think differently and try to change things - have always been called troublemakers.” 

“My cigarettes and I are going outside. At least they show me respect.”

“Some people read books for fun.” 

“People who are crazy rarely question whether they're crazy.”