It takes weeks to months for antibodies to herpes to be formed. If he had a positve IgG test a month after the rash, about half of blood tests for HSV would be positve. thus there is a possibility that he already had herpes but was unaware.
Either way, if he has herpes and you do not, you need to take precautions to make sure that you do not get it. This includes condoms and preventative therapy for him. EWH
Thank you for your time. I am not quite sure I understand your answer. Just to clarify my information, one month after he had the episode he went to his doctor and they said it sounded like genital herpes and they did an igg test and he was positive. They said the rash on his back and legs were probably related to something else besides genital herpes but it went away in a few days and has not come back. He had not been tested for genital herpes until December 22nd 2008. He did state that he dated a girl ten years ago that could have had genital herpes. I hope I explained myself properly.
Let's get straight to the question which you ask which, if I can re-phrase it, is whether or not your BF's symptoms which included a genital rash suggestive of herpes might have been a primary or initial episode of herpes. This question will, in turn inform your own concerns about the possibility that your partner might be unfaithful to you.
Straight to the question. Your BFs rash was not an episode of initial genital herpes and is unlikely to be a recurrence. The reason I say this with confidence is that you have told me that he already has HSV-2 as indicated by a positive blood test. When persons have HSV-2 they do not get re-infected and the characteristics of the illness you describe are too extensive for a herpetic recurrence. Thus it is far more likely that his symptoms and rash are due to something other than herpes.
A few other comments. If your BF has HSV-2 as indicated by a positive blood test, whether or not he has outbreaks that he recognizes, and you do not, you are at risk for infection from him. The fact that he has a positive blood test means he has HSV-2 and if he has HSV-2 he does have occasional asymptomatic shedding of the virus which could be a source of infection for you. Many questions about herpes and prevention of transmission can be obtained by accessing excellent informational web sites such as the one run by the American Social Health Association (disclosure, Dr. Handsfield and I are both on the Board of Directors of ASHA).
Hope this helps. EWH