Hello. Thank you for writing to us at healthcaremagic Hsv or herpes simplex virus is usually transmitted by close/intimate contact with an infected partner. The infection can remain clinically silent for weeks or months in those who have the virus, however, they can still transmit the virus unknowingly to there sexual partners. The reason being that, Hsv is continually being shed in low doses from infected skin surfaces, even during clinically silent phases. Both, these factors i.e silent infection and asymptomatic shedding makes it impossible to know the source of infection, if either you or your girlfriend have had previous sexual contacts. Since you have been in a relationship with your girlfriend for past 3 years therefore it is quite logical that you also get tested for herpes as well. Regards