How to break it off with someone?

I posted a question a little before and most people answered what I already knew in my mind. I have to leave my FWB. But I have never had a FWB before him and I've never broken things off with anyone before, I don't know what to say, how to say it, when to say it. Should I be with him one last time to make it easier or not even see him and tell him over the phone? I already tried a fade out and he put more effort into contacting me. Please tell me how to break up with someone. (Even though we aren't "together", you know what I mean)