In this situation, I'd send him a final quite bland text to say
"Hi, thanks for the date (don't bother mentioning the sex), just to let you know I'm calling time because I'm seeing someone else. Good knowing you, all the best"
Make it decisive and resolute - then block him, don't get tempted to get pulled back in if his poor little fragile ego is dented and he comes back whinging.
Do it 100% for you, it will give you a feeling of closure, you've pulled stumps not him, and it'll wipe the smug smirk off his face. Also you're not making a point you're giving him some facts that he can't argue with.