No, that's not true.
Obviously some people are more likely to go abroad and have sex with holiday strangers than others, but the majority do not. Some people will use it as an excuse but really getting drunk abroad doesn't 'change' who you are any more than getting drunk in a pub in Slough, aside from the relative anonymity (you'll never see 99.99% of these people again, and 99.99% of them have no idea who you are).
People who go on holiday and cheat are the type who'd cheat anyway. If someone isn't the type to cheat, they won't become the type on holiday (unless they're using being on holiday as an excuse).