Good on ya for saying what you thought. That's good. 100%
@Stanley is right, though - I missed the part about the ex. Rip off the bandaid. The fact that you pushed that urge down when you found out what she was doing a long time ago fixed you on a downward trajectory.
Women instinctually get romance in ways guys don't - an
exclusive, intense bond that cannot be broken. (uninterested in debates on this definition - there are nuances and contexts)
So with that context, the fact that
they are so absolutely dead set on locking down a guy to be exclusive, when
they do something shady and then he overlooks her directly cheating on him they
know that a side of that man that demands respect isn't coming out. He isn't respectable, so they push and they flip that instinctual energy onto the guy: She dictates, she dominates, she lays the blueprint for how everything's goin down - and he sits there and submits and takes it.
Your energy isn't that. You're raw, powerful, dominant, and don't deal with bs. She needs to learn that doing things like that has consequences and what she's doing now has consequences.
Tell her her crime and the sentence! - Tell her what she did wrong, and break up with her. Refuse her framing decisions, values, etc. She's cheated on you and now expects you to be cool with going to a party island with a dude.
This sucks to say, but she's sucked in by the flights, and everything else you're doin for her. Rip it off. Do it.
p.s. if that ticket is coming out of your pocket... cancel the flight. "You aren't paying for anything." If so, do it before you talk to her.