#20684
You should tell before kissing or sexual activity. Don't use the word herpes, just say you have the cold sore virus. If the person like you for who you are there shouldn't be a problem.
The only restriction is that it kills sexual spontaneity. By the way is it oral type 1 or genital type 2 you have? I had girlfriends who had type 1 and never got a cold sore. Unfortunately, I got herpes 2 from my wife last year, and have had many painful genital outbreaks. My wife didn't know she had it.