Thanks for the question. HSV or genital herpes is a very common sexually transmitted infection and perhaps the most spread disease through sexual means. Of these, type 1 of HSV can be transmitted orally through oral sex, kiss and any sort of saliva exchange between infected and non-infected people. It can even happen from childhood, through oral contact between parents and children. There is a dark side for HSV type 2 infection, which causes genital herpes. That is, it can stay dormant in most of the infected people, say 80% of the infected. Nowadays, it is one of the major health concerns, affecting millions of people year after year. The only proven method of preventing the spread is abstinence of sex with infected people. To reduce risk of transmission and to suppress visible outbreaks, antiviral medications are administered. As the infection stay dormant for years, finding the age of infection is nearly impossible. But the family doctor may be able to help you by examining previous medical history of your girlfriend. As I told, there may not be an evident outbreak of virus and mostly you also might have become a carrier of the virus. So, it is better to do a lab test for you too, to rule out a possibility of getting infected. Lab tests can reveal presence of virus and thereby say whether you are infected or not and simply cannot be used to date the age of infection or find from whom or when you have got infected. Hope my answer helps. However no treatment for cold sores or treatment for genital herpes in general, is found to be effective in eradicating the entire disease. Best of luck.