I don't want to go on vacation with a girl after she brought up the fact she's going to hang out with her ex 2 weeks before we go.
When's the trip?
One day. I haven't prepared myself for the breakup
Why'd you wait so long to figure this out? 24 hours before you leave and you wanna bail on the plans. She's gonna be angry. Is it too late for her to change plans?
She said there can be a last minute change
Then maybe you're off the hook. Tell her you don't want to go, but be specific about your reasons.