Struggling with partners addiction

I am struggling with my partners clear sex addiction which he refuses to admit or get help for. We have been together for three years and he cannot stop going behind my back through lust. He constantly watches porn, buys content, messages other people sexually, enquires about escorts. We had a conversation as our sex life had dipped. He said he just doesn’t feel the need to with me and the sexual attraction has dipped yet he’s constantly watching porn and looking at other women. I don’t know what to do anymore