I'd say it was that black and white. If I think someone will cheat on me, I don't waste my time dating them. Occasional fleeting doubts are normal of course, but not to the point of ultimatums and banning a holiday with his friends.
If you seriously think your boyfriend will cheat on you, to the point you behave like the OP, you shouldn't be with them. Right, and the kind of person who makes "drunken one night only" mistakes isn't any more likely to make them in Amsterdam than anywhere else, surely? What possible reason is there for the OP to worry he'll cheat in Amsterdam, but not anywhere else? Does she ban him from going on any nights out with his mates if she isn't present? There's no shortage of booze, single guy mates and easy ladies in the UK, why does it being 'a strange country' make it more likely he'll cheat?
If it's prostitutes she's worried about, she's an idiot. If he isn't the type to cheat with a girl in a club, I'd say he's even less likely to pay for a prostitute. And even if he was the kind to cheat,
it would be safer for him to cheat with a prostitute, because they insist on condoms, get regular STI checks and have no interest in their clients once the deed is done. The RLD in Amsterdam is pretty strongly regulated, these aren't risky women like they would be in the UK. Compare that to a girl in a bar who won't necessarily use protection and had no proof she's clean, and who might turn up later and cause problems for the OP and his girlfriend.
The RLD is the place in Amsterdam with the best nightlife (and that isn't a euphemism for banging hookers) and so that's why they're staying there. The prostitutes are usually not massively attractive, and they're not doing anything slutty in the windows to lure your poor innocent boyfriend into paying for sex with them (ie you'd see more slutty behaviour in a music video). In short, anyone who has actually been to Amsterdam will tell you you're overreacting. And I think that says more than people who've never been
spouting their preconceptions of the place based on the fact there's a few hookers in windows