General advice given here is to reward good behavior not try to buy it. Guys are told not to even buy dinner till sex has been had or, at least, major headway has been made. And here you are booking a trip out of the country with her? I realize you are splitting it, but that's not the point.
The guy above is being charitable, IMO. Guaranteed, at some point in time AFTER the trio is booked, paid for, not cancellable but BEFORE you get on the plane some sh1t will happen. A fight. She will flake. Something. And if I'm wrong about that some sh1t will happen on the trip. Guaranteed.
You are jumping thru little hoops for a woman you've already been with for six years who won't have sex with you. There's something very wrong with that picture, you are just in that deluded state that we all get in, but you know enough in your gut to post here about it. I have a friend who did this stuff serially for 15 years till he finally got married. I watched him eat more trips, weekend getaways, wind up with more puppies that were supposed to be gifts.....you name it....even had one move in his place for 3 months because she got kicked out of her old place...never had sex with him but racked up thousands on his delivery food accounts.. you name it..because he was trying to win over a situation that was barely even for real to begin with.
Your woman sounds confused. And you sound like you are trying to be captain save a Ho. You can't save them if they don't want to be saved, bro. She can say anything...none of it matters....6 years and she won't have sex with you is your red flag, right there.
We aren't trying to be harsh. We are trying to slap you with some reality so you get out of your own way. We've all been there and we know firsthand that guys are notorious for deluding themselves at times like these because they want a particular outcome.
You need to get a handle on this situation pronto, just for your own sake. For the love of god, do not book a trip with her until you do.