Why would she tell me about her hookup?

I'm still friends with my ex and we talk a lot

We haven't been with anyone else before we dated

Recently she told me she met a soldier on the subway and they hooked up, when I asked for more details she was open but then she suddenly got shy and now she really doesn't want to talk about it

The soldier is gone by the way, he was deployed shortly after they hooked up

Why would she tell me about it and act this way? The way we were talking, and still are talking, it's almost like we could start dating again, so I don't understand

Why would she tell me about her hookup?
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