You realize that having someone tell you the truth all the time, every single time is just as likely to end relationships.

That's why "white lies" exist. Do you really tell your best girlfriend that she looks terrible in that dress? Or do you redirect her attentions?

That's kinda what OP's fiance did here, look at this terrifying option of an isolated cabin full of men and alcohol, where so many things may go wrong and help would be far away...now look at this other option where we're in civilization - in a gorgeous city. He kept it from her till the last minute and replaced it with something that (to a rational person) is a lot safer and more tame of an idea...that should deflate anxiety in normal people...like if someone dragged you skydiving then switched it to one where you were floating in that giant fan tube instead. But if you read OP's latest comments, she basically has issues with Montreal too.

That's not on the fiance, that's on OP. When people cannot tell you things because they know you'll react badly, that's just as unhealthy for them as it is for you.