Spirit Bound by Richelle Mead.

After a long and heartbreaking journey to Dimitri's birthplace in Siberia, Rose Hathaway has finally returned to St. Vladimir's-and to her best friend, Lissa. It is nearly graduation, and the girls can't wait for their real lives beyond the Academy's iron gates to begin. But Rose's heart still aches for Dimitri, and she knows he's out there, somewhere. 

She failed to kill him when she had the chance. And now her worst fears are about to come true. Dimitri has tasted her blood, and now he is hunting her. And this time he won't rest until Rose joins him... forever.

...

This book was really amazing. In the last book, I was devastated. 
But then, Dimitri comes back from being Strigoi. Of course, if anyone can come back from that, it would be Dimitri. 
One thing that really irritated me in this book, was how Rose went through Hell and back to save Dimitri, and yet he gave all of the credit to Lissa!

I mean, I love Dimitri, and I understand that when he came back, he was going through some things, but really?!
Things Rose did for Dimitri:

• Dropped out of school, after she just barely told she was going to be able to graduate. 
• Abandoned her best friend, along with almost any chance of being her Guardian. 
• Went to Russia to try and find him. 
• Faced down countless Strigoi for him. 
• Was used as a blood-whore.
• Broke into a maximum-security prison to free her enemy.
• AND MORE. 

Things Lissa did for Dimitri:

• Charmed a stake. 
• Staked him. 

...

Rose did so much for him, and he gave all the credit to Lissa!
And Lissa should have helped Rose do whatever the hell she wanted after all she's done for her!

Besides that, it was a great book. :)