I have just come across this entry - and although its an old one, it's still searchable, so I thought I would add an update and some personal experience for worried people out there.
It is possible to contract herpes and have no symptoms - very unlikely, but possible. Most likely the herpes was contracted some time ago and might have been dismissed as something else (Thrush maybe?), or possibly just a bout of flu.
It is possible to pass on the disease without having symptoms present at the time. Herpes is quite intrusive in the body but your own (healthy) immune system can fight it reasonably well. However, even if you have no outward symptoms (possibly your body might tell you by inflamed lymph-nodes or flu-like symptoms, but not always) the virus can actually 'shed' through the skin (viral-shedding) and possibly - given the right contact, at the right place and the correct entry point - infect a sexual partner (of either intercourse).
So it is possible to contract, pass on and infect someone without knowing you have it... ...although very unlikely, think back to early sexual contacts you might have had for clues.
BTW, It is also possible to have a full sexual health screen and not pick up the herpes - when dormant the disease hides in the lymph-glands and at the end of nerve cells and you could appear herpes-free on blood tests.
Now the important bit: Herpes is not a death sentence, it is easily treatable these days and there are a couple of very good medications available which will keep it at bay. I have had herpes myself now for possibly greater than 20 years and, although I have had outbreaks during periods of stress in my life, I have not really had an impact on my life. I take Aciclovir twice daily (have been for close to four years now) and have not had any episodes of herpes in this time. I have also had unprotected intercourse with long term partners in this time and not passed it to any of them - such is mine (and their) confidence in the acicolvir.
There is a stigma attached to herpes which need not be - yes, agreed, its better not to have it and to have been sensible in those early (heady) days of my youth.. ..but it's not that bad. And I will always make sure I tell a potential partner (and anyone else who will listen) about my herpes BEFORE we start any kind of sexual relationship (with or without protection).
If they have a problem with it, then so be it, but at that point it's their choice what to do. Never hide these things even if you have no symptoms.
If anyone would like any more information - just shout