Maybe you need to cut him loose with this fear and let him manage it himself? After all, it’s not like HE would be the one pregnant here, and YOU are the one now having to bear the physical burden of extra (and unnecessary, as there was nothing your pill wasn’t already doing that Plan B could add save a burden to your body) hormones.
Personally, I would kindly let him know he needs to back off and manage his own feelings from here, were it me. And perhaps reevaluate his readiness for this kind of sex given this, and let you know if it just doesn’t feel like something he can handle right now, with the reassurance that of course that’s okay, if that’s the case. That’s my two cents.
Never doubt that a small group of thoughtful, committed citizens can change the world. Indeed, it is the only thing that ever has. - Margaret Mead