So I'm imagining a scenario like a previous prompt, but instead of Essek being the one to fuck someone to keep their cover, it's Caleb. Basically Caleb letting someone use him, because after his Scourger training, he just doesn't really care that much about trading sex for.. anything really. It's just mechanics, it's only his body, so long as they don't really hurt him, he can just check out and rely on muscle memory. He feels like he doesn't deserve more than being a means to an end.
Maybe he sleeps with someone to get information that will help Essek or to provide a distraction for him. Maybe someone is making Essek uncomfortable, and he steps in and draws them away so Essek won't have to deal with it. However it happens, Essek is horrified, not that Caleb would casually sleep with someone, but that he regards himself so little. Essek then makes it his own mission to show Caleb just how important, how worthy of consideration, he thinks Caleb is.