Why did she get so upset about this?

We've agreed that for the time being it's impossible for us to date seriously because of the distance. We live in different countries.

Then we were chatting earlier today, and I mentioned that I was going out tonight. She asked what I was planning on doing, and I mentioned a woman I'm dating.

She got upset, said she doesn't want to hear about it, and told me she had to go?

What's going on?
Why did she get so upset about this?
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