Hmm, I'm sorry it was so disappointing. There was obviously a misunderstanding. She thought she was just meeting a friend and you thought it was something different. Unless she made up the Vegas thing just to put you off but keep you as a friend. Did she offer to split the check. If she didn't then I don't blame you for feeling used. There is a difference between generosity and being taken for a mug. I know the feeling. I wouldn't think much of a friend wo expected me to pay all the time.
You have your travel meetup group to look forward to.