Let me see if I understand this.
Your girlfriend and her female friend (who I assume she has no sexual interest in) talked about sex. This made you angry, although it was a joke.
Then in some other capacity (help me out as I have zero context here), you ask questions and your girlfriend gets angry about that. It depends on the questions and your tone. "Do you like sushi?" is not exactly a question one should normally be angered by. "Why are you so fat?" or "Who do you think you are?" are going to questions that'll anger pretty much anyone.
Then you asked if she wanted to leave, she said she didn't know. You responded, "How do you feel about this?" and she said "I don't." You professed love and that you would respect her decision.
And now you're here.
A few things.
- Good lord, you overreacted about the sex talk thing. People talk; this clearly meant as much as the two of them trading homework answers. Let it go.
- With no information about your questions, I can't figure out who's being reasonable, or not.
- If she says she doesn't know if she wants to leave, and she's not sure of how she feels, maybe the thing to do is to give her some space and see what happens.
I get the feeling you demand answers a lot, and you hover. That's what it seems like from here. But you tell us. What could two people, who aren't interested in each other sexually, talking about sex, could possibly hurt you? Was your girlfriend giving away bedroom secrets? Or were they talking about who they'd do if they had the chance? Or were they discussing a problem the friend was having?
See where I'm going with this?