Let's be clear.

I have- had a friend, whose name is Rob.

Rob is a cokehead.

Rob has an exgirlfirend who shahll remain anonymous for this post. She is also my friend. She used to be a sex worker.

Rob tried to convince me that I should stop being her friend because of her past, and he implied I should stop being her friend on the grounds of my religion

DUDE HAVE YOU MET MY RELIGION?  That is NOT what it says to do.

So I'm not his friend anymore.