Tiresias, I think she's simply frustrated with the world. You know, like, "Aw hell, another complication in the complicated world of poly-dating?" No judgement on anyone afflicted with herpes.
It can be really frightening to think of leaving a safe, established sexual relationship and open yourself up to the possibility of getting something through another partner. Definitely enough to frighten me off. And if you're allergic to latex, my understanding that the sheep-intestine alternative does not provide a barrier to some STDs.
Anywho, so that I don't completely hijack the thread, I think you're completely right in taking it slow. It's worth it to be absolutely sure where you're going before making a commitment. I'm glad to hear that you seem to have such a level head.