Girl I'm dating stayed up till 6am talking with a guy she used to have a relationship with?

Been seeing each other for about 6 months, we are exclusive, but not official yet. She just texted me casually that she was tired cause she was up until 6am talking to a friend overseas. I asked where they lived. She told me the netherlands.

She has mentioned this guy before, and that they have dated/hooked up and she would have an open relationship with him if that is what she wanted one.

I don't know how to feel about this. We have been having some issues lately, but have resolved to fix them. And then she just drops this like it's no big deal. I find it deeply disrespectful. Given the context of their relationship, and what she has told me about him.

How should I handle this? I am fucking pissed, but not sure if I need to ask her what they talked about first. But doubt she would tell me if the convo got romantic or sexual at all.
Girl I'm dating stayed up till 6am talking with a guy she used to have a relationship with?
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