It can be exhausting when they want to be at it non stop.I usually suggest a "break" in a jokey way,let me catch my breathe! that sort of thing,have a drink,etc.Try other tactics such as a massage,if you do his whole body it can kill some time lol.
Having said that if you are not happy with a booking then don't do it,it will only leave you feeling like you are now and that is not worth all the tea in China.