Are my extra precautions around pregnancy and STIs reasonable?

I’m pregnant and one of my partners is looking for new connections. I am absolutely terrified of contracting herpes during pregnancy as an initial infection can cross the placenta and cause stillbirth. Would it be unfair for me to tell my partner that I will not be physically intimate with him during my pregnancy if he chooses to be intimate with a partner who is HSV positive? I know that herpes is common and a lot of the stigma is unnecessary, but I’m not willing to risk my baby’s safety.

No, that sounds entirely reasonable. Everyone gets to decide what their own risk tolerance is. Pregnancy is a specific health concern that requires extra precautions. You are not being unfair or stigmatizing, and if your partner insinuates that you are, or tries to argue you out of this perfectly understandable boundary, they’re the one with the problem.