There are 2 possibilities.
1.The levels in the body vary it goes up and down ... I had gotten negative for HSV1 and then an equivocal then a negative, I am not sure if this is because of having chicken pox when younger but I know that would not cause a positive result.
2.You may have just gotten the virus, I suggest getting retested in 4 months just to make sure you are negative.
I am not sure of your relationship with your partner but if you both have been together for more then 4 months and he is negative... I would say you have nothing to worry about.