It is very possible that you do not have it. Everyone that is in a relationship with a person that has the virus is not guaranteed to get it. Also, the transmission rate from female to male is low. I was with my ex-husband for 4 years never used condoms and he never got, my ex-boyfriend never got it and my current one either. I remember speaking to someone that had the virus and she and her husband had been together for over 20yrs and he still never had gotten it from her.
Also, not everyone has text book symptoms or outbreaks. Sometimes people push an outbreak aside as a yeast infection or jock itch. Not to mention an estimated 80% of people that have genital herpes do not even know they have it.. so when they say "generally" it seems as though it applies to less than most.
So please trust your girlfriend if you had never had a reason to believe she cheated do not start now since she must have gotten this before your relationship.
Just a quick question do you know which test you had?
Hope this helped
If you have time there is a thread at the top of this board called "Happy Couples" there are many relationships on that thread where one person has it and the other does not.