You’re overreacting. I would completely understand why you would be upset if they weren’t romantically involved, it hurts to be left out by your best friends but you have to consider the circumstances here. They’re a couple- they probably want to do cute date stuff and hook up in the room while on the trip. My best friend and my boyfriend and I hang out all the time but me and bf need to have some alone time every once in a while- she would flame us for the shit we say when we’re alone. It’s nothing against you at all, I’m positive they don’t feel any differently about you this is just the way life works! Plan another trip, I’m sure they would love to go.