What she is suggesting is not cuckold. Cuckold is when a man allows other men to fuck his wife or gf and watches. But Today it also has an added meaning to describe weak willed men who can't do anything to stop his gf / wife from having multiple affairs against his will. Either way you need to weigh up is what she's offering a waste of money if your just gonna sit in the corner and wank
There's also an element these days of the wife/gf not being satisfied with her husband's small white cock and therefore has to find "bulls" who have a big black cock as that's the only way she can be satisfied. This also comes with humiliation and insults such as "you're not man enough to satisfy me" etc. Apparantly *some* cucks also clean up their wife (RO) after she's had a BB session (always BB with these cucks), which adds to the humiliation aspect (although I don't know if this is ever more than fantasy for most people). It's ALWAYS a ripped black man with a massive cock during roleplay/fantasy, I've never known a man wanting to role play his wife having affairs with Asian men, for example (that's not to say it doesn't happen, I've just never yet known anyone's fantasy to involve anything but black men).
I'd say the OP can expect to watch the WG fuck herself with the dildo, telling him he's not ever going to be man enough to satisfy her, hence why she's fucking this BBC and not him, and then he gets to act out being grateful she lets him "clean her up" or stick his pathetic white cock in after the real man's been there.
I'd be interested to know what actually happened during the session (after the booking, obv).