My best friend suddenly stopped inviting me and hides her stories from me and I don't know why she would do this, I don't know what to do with her?

I had a best friend with whom we were very close, we helped each other and talked everything. She is not living in my city because of university but she usually comes some weekends or sometimes stays there, and we used to go out a lot at night with another friend of hers, but I noticed that her friend left me aside or ignored me and I found out that she has talked behind other girls' backs so I suspect she might have talked behind my back to my best friend. But lately I noticed that she was rejecting my plans to go out at night because according to her "she didn't like going out anymore" although we continued talking without any problem, and a few weeks ago I found out that my best friend went out with her other friend but she didn't even invite me, and she didn't told me that she was coming to my city that weekend, and the worst of all is that she uploaded a story on Instagram and hid it from me (and I was able to see it through another account) but since then her behavior bothered me, and a few days later she spoke via text, but I ignored her because I knew she was going to pretend nothing had happened or make some stupid excuse. And now, a month after that time, she spoke to me back and I responded but I don't know if it's okay, because I don't know what to do and if I should stay away from her or how I could talk about what happened….

My best friend suddenly stopped inviting me and hides her stories from me and I don't know why she would do this, I don't know what to do with her?
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