Yeah, I read that part. I'm so pissed, especially when Zoey yammers on about how she and Blake are in love and have a connection. -_- Kristen Cast tries to handwave this in this book Nyx in the House of Night, by explaining that in the Days of Yore, polygamous relationships were fine and thus vampires still practice them. I honestly don't know if it was intentional or not, but given that Erik is the only one who is bothered by Zoey cheating on him, it implies that he's just a poopy-head for wanting a monogamous relationship. -_-