You are reacting to your painful experiences, not any meaningful risk of criminal exposure for the boyfriend here.
I have no idea what crime you imagine is at issue here.
He has no "criminal intent" if he does not know of the girlfriend's occupation.
You are imagining arrests over nothing.
It is, I suppose, possible for an arrest to be made if some WAY overzealous prosecutor just wants to be a prick and invent a charge to try and force a confession out of her. There certainly would not be a conviction of the guy. What evidence of his knowledge and intent do you imagine exists?
There is obviously no pimping - he does not even know of the woman's occupation!
Your reaction is pretty ridiculous in terms of imagining some criminal charges.
That said, I tend to agree with your reaction to her lying about what she does to him. The emotional risk for him is obviously real. That is another matter entirely