Why is she upset with me?

Have been freinds with this girl for a little over 3 years we used to text frequently but here lately she's just half way responding not engaging like she used too and dosent reply sometimes till hours later. So I stopped messaging her and haven't heard anything until recently a mutual freind had told that she was upset that I don't message anymore?

When I did message it was like she didn't want to talk so why would she be upset?

Why is she upset with me?
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