Reddit is insanely misogynist; probably one of the worst places to post about something like this. And yes, their mods will delete a thread if there are too many unapproved responses (anything not totally male-centred). Also it's useless for any type of practical/legal/policy advice unless you state your location and someone familiar with it happens to see the post.
LOL at this: I would have said not the asshole but you wanting to share a room with a man, your boyfriend, but not her changed my mind. It honestly just sounds like you see her as a man and don't want to share a room with her. I find there's a difference between sharing a room with someone I'm in a consensual relationship with versus any random and especially one who gives me creep vibes. Consent exists even if it makes you mad, bro.
I think the safest thing to do is for her and the bf to identify as a specific third gender - nonbinary would do - for the duration of the trip, that way they're sure to be paired together as there are then two of them and no other people in the category.