Telling a girl you have an STD

Sorry if something similar has been posted before, I'm not really an OOT regular. I was just wondering if anyone here has had experience telling a girl (guy) that he (she) has an STD. I recently found out that that I probably have herpes (apparently the test for this isn't totally reliable, however the [censored] you want to take that). Anyway I figure being up front about this sort of thing is the best course of action but I'm not really sure of what point in a relationship you tell someone about this and how you go about doing it. I'm not dating anyone right now but I worry about how this is going to screw up my future.

If this matters at all...I'm not a terribly promiscuous person. I believe that I contracted it from unprotected oral sex with a girl that I had been seeing for a few months.