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Sad to be said, but your friend created and triggered your feelings of bad anxiety, and this scene could have been avoided had your friend included the ex would be visiting with her. I see that you deserve an apology, at the least, and this should come from your girlfriend.
Really, it appears that she was pulling a "show you" moment. And I don't really know what type of friendship you have with her; yet friends don't do dynamic acts that cause others to feel unsafe emotionally. Friends express love and care through what they show you and what they say. So if she can say that she is sorry for hurting you and putting you on display in front of the ex, then perhaps she meant no real harm, and in the future you may each have a clear understanding of what her intentions are. Move carefully and reflect on what you expect that's comfortable for your own feelings.
Much love & hugs!
If you are not as close as before, she was most likely smirking you; she wanted your heart to pound, and that's not friendly behavior. I sort of think that she is still trying to figure if she likes the ex, and she brings him around you to see if he's interesting enough to decide to wed. Cat and mouse type of behavior. Girls did this type of stuff when I was a teenager. Gosh.
I really hope the best for you and this gal :-) Just raise your eyebrow, tap her on the shoulder and say, "Just what was you up to bringing dude around?" And I'd wag a finger in her face too, lol! She's got it coming to her! Just ignore anything else she suggest with the ex. I imagine it's the green-eyed monster that she's looking for in you, which adds more interest in her mind for the ex, just not worth it at the risk of hurting you. She knows this.
Enjoy your time for the rest of the day!