Looking for input on how people calculate risk of herpes with multiple sex partners, given that it's not always on STD panels, the panels can be inaccurate, and it can be passed without symptoms.

Me and my FWB are open to multiple partners; earlier we were exclusive and having unprotected sex, and recently he kissed and had reciprocal oral with someone else (who says their panels are clear, and I trust that's true with like 5% doubt). I don't know how to decide what activities we should keep doing together before and after he's tested.

Let's assume: even between people with no herpes symptoms, all unprotected sex (and kissing) comes with some risk of herpes transmission, and I have already accepted that risk with him and his sexual history when we were exclusive.

His unprotected oral came with risk of herpes transmission, but an STI panel likely won't test for that or could return false negative anyway.

From a herpes standpoint, testing between each new partner is useless if it's not on the panel, and you're at some risk even from 'safer' activities like kissing, penetration with a condom, and oral with a barrier. So how do you calculate how many unprotected sex partners is too risky? Or even number of kisses with strangers?