tessa,

Not sure how Ms Ruby will take it but I liked it. TYWD pointed out quite a few verbal gems and you do seem to be developing a way with words.
"The individual doing the deed," was indeed giving it away a bit and any number of descriptive alternatives are available.

Now to the plot twist. Your readers are going to have one of two reactions, (maybe both) either "Wow that was clever!", or ""The bitch is trying to make a fool of me!" you probably are aiming for the first and not so much for the second.
You've handled transitions well throughout the story so maybe you want to be extra clever on the final important one.

Only when the cock slid completely out of the girl’s slack-jawed mouth did some of his awareness return to him, along with some frustration.

“Fucking bitch,” he muttered. “Could’ve made it last ‘til I shot my load.” Ok at this point your reader knows he's mumbling to the passed out victim, but is he really?

He motioned for the waiter to bring his tab. As he waited, his beautiful slut walked towards him,Before you put that swinging plastic dick on his sub why don't you throw another quote in, this time leaving no doubt he's addressing his sub. Have him berate her for not making the show last long enough for him to get off.
Now your reader is a bit confused still thinking his sub was the victim but bits of the scene are not adding up. It's sort of a subtle warning before the plot twist

Still need to do the transition, place that dildo on his girl,not in her, but do it with a clever turn of phrase that leaves the reader saying"Of course" instead of "What the fuck?"
her strap-on cock still glistening from the leavings of the blonde’s mouth. When she stopped beside him, Jake stroked her cheek as she gazed adoringly up at him.