Why Did Nick Keep the Fact that he was a Vampire Away From Tracy?

Think about it; she already knew vampires existed, so it's not like Nick being a vampire would have been a huge shock to her. With Schanke, it made a lot more sense to keep it a secret, because, well, it's Schanke we're talking about here. But with Tracy, if anything, it was probably counter-productive due to the fact Nick had to go around her whenever she or he dealt with Vachon. Thoughts please.