I recently went on a civilian date, and after some thought decided to tell the guy that I’m a sex worker. He seemed OK with it, but when we parted he said he had to ask his primary girlfriend how she felt before deciding whether to go out with me again. I told him I didn’t think it was cool for him to out me to his girlfriend; since they’re polyamorous anyway, she’s already agreed to his seeing other people and I can’t see how my profession should make any difference.
I personally have never dated men socially while actively whoring; the one exception was Matt, and he started as a client. So my answer is drawn from my sense of ethics rather than from my personal experience. In general, it seems to me that the proper schedule for telling a new relationship about anything controversial or potentially problematic would be the third date. I think the first date is just a bit too soon; if there’s no chemistry you probably won’t make it to the third date, and then there was no point in telling him about it. But if you wait much longer than the third date, it could be much more uncomfortable or even painful for both of you if the outcome isn’t good. I do realize that most people ask, “What do you do for a living?” within the first ten minutes of the first date (if not earlier), but I think you’re justified in bending the truth a bit so as to avoid the subject until a better time.
Regarding the second part of your situation, though, I think your judgment is exactly correct. If his girlfriend is all right with his dating amateurs, there’s no reason it should matter if he dates a professional; as we both know, the chance of STI exposure is far less with a whore, and I think it’s not too far a stretch to say that we are also more likely than even most polyamorists to treat the issue of multiple partners with good sense and maturity. Simply put, it’s none of his other girlfriend’s business what you do for a living, and if he insists on telling her despite your request to the contrary it could be an excuse to refuse a second date without having to admit his own anti-whore bigotry, a sign that he isn’t nearly as polyamorous as he pretends, or both.