I asked a GF early on if she had any STDs. She said no. A few months later it became obvious she had cold sores. I considered myself lied to, but it was a rather venial sin. I can understand people not mentioning it if you don't have an outbreak. As soon as you get an outbreak, though, you might want to mention it. You should maybe then try to cover it up with some pseudo scientific claim that everyone has herpes, but not everyone gets outbreaks. Then it sounds like you're just not very well researched.