how can I put this in a mature way?

My fiancé has a friend that's obsessed with porn and sends my fiancé pictures of it.. yes I'm very insecure so save them comments about me being insecure over it. But it's so annoying being on his phone looking at something he is showing me and then it popping up. It makes me furious.. this friend has always had something wrong with me and has actually said stuff about me to him. So asking his friend nicely to stop is out of the question. I told my fiancé would he like it if my girl friends sent me pictures of dudes naked he told me to stop and that he wouldn't like it. But why am I to be the one responsible for telling my friends please don't do it when he can't even say it to his? I'm honestly sick of it.. so ladies or gentlemen how would you ask this to stop and how would you react?