Dude, he’s fucking the girl you jack off to. That’s the exact opposite of being cucked.
The comments are full of people going “it’s not like they’re having sex in these examples or anything” so I’ll go ahead and bite the controversy bullet and add:
Even if a sex worker partner is having sex with clients, it’s also literally just work. It isn’t morally wrong. There is nothing wrong with it if both parties in a relationship are aware of the work, and if everyone is being safe.
Sex workers who have sex are no worse or “dirtier” than sex workers who provide other services.