That's pretty funny that you call her your "wife." I always assumed one has to marry his wife. I can see it now, high school kids all over are going to have "husbands" and "wives" after dating for a few months. Soon after, liberals all over the country will be seeking legislation to cover "light" spouses (a person who is a "husband" or a "wife" without having been legally married).
No, the tax laws do not cover live-in girlfriends. Does she file her own taxes? I'm not trying to be jerk, I was just floored by the question.