Ahhhhh, we have something in common here, although I learned to scale it back.
We expect people to treat us as we would treat them. The thing is, people don't always think like us and that doesn't make it right or wrong. You had a picture of how things would go when you asked her out on a date, and she had another. To her, it's a casual first date and she may be wanting to date around. You are meeting up with a bunch of guys and girls, and interest may be taken in more than one guy, or girl for that matter. You have no commitments to each other.
Dating is what it is. There is really no level of loyalty on the first date. You are triggered because you know the other person. You would have no clue if she was doing this if it wasn't a person in the group. And she could have a bunch of different dates lined up for the weekend just as you could.
Hang in there. You'll find what works for you, what are willing to accept and what your dealbreakers are. And they will change from time to time.
