Thank you again for your kind and thoughtful words. A few of my close friends have said "I think you know what you need to do" and what I've heard here seems to echo that.
I am still afraid FOR him, too...the last time we talked, he seems to be justifying his possible involvement with this person, for instance: "Well, people who have had it longer don't shed virally as much, and X percentage of the population has it/has been exposed to it, and she had a partner for X amount of years and he never got it..." (oh? How do you know? How does SHE know? Sigh.)
I have explained to him that one of my former metamours contracted HSV genitally, from oral sex, and that this is part of the reason that I take this extremely seriously. From what I understand, it can be painful and debilitating and I do not want to risk that happening to me.