You find his talk about sex with his girlfriend distasteful. So tell him that you find it distasteful, that it is too much information.
If after that he keeps on informing you of his sex life (rather like a small child telling anyone within hearing distance that they have done a poo!) then it is because he enjoys boasting about it. If you don't call a halt, it is because, secretly, you enjoy the second-hand thrill of hearing him.
You know how to stop this, so why tell us about his calls and his news flashes about his sex life? Probably because you are enjoying the discussion - as much as you enjoy chatting to him.
Unless, of course, he doesn't exist, and what you are enjoying here is telling fairy stories about a fantasy? Why not write a novel instead, that might even become a best-seller and make you famous.