Can anyone help me find this book?

This is more or less the plot. There is this book about a girl who went to boarding school in Canada and when she gets there she gets a boyfriend but he couldnt please her so she killed him. And she feels like a hero when killed him. Than she got another boyfriend and he couldnt please her either so she killed him too. And than this boy figured out what she was doing and thought she was a terroist and he wanted her to help him blow people up but she killed him because she was not a terroist and finally she got a boyfriend who could please her but he left her for another girl and im not sure if she killed him or not but i remember she threw her favorite teacher out the window because he wanted her and than she said she was going back to America