Why does this make me nauseous?

Why does talking to someone whos done something disgusting, and borderline evil, make me feel nauseous and feel sick?

Btw i say evil because this person i a convicted pdf. But he has done other disgusting and disturbing things but thats one of the worst ones.

But he messaged me earlier and i havent spoken to him in years. I didnt even realise he followed me on social media, but like my only words i said back to him was 'not so kindly fuck off you disgust me'.

I cant stop the feeling of disgust i wanna cry also how do i stop this?