Am I being very jealous?

Hello, today I wanted to vent something about a specific topic. To understand things, I am going to tell them from the beginning. I have a girlfriend and we have been around for a while, and it turns out that at my school they are going to do some dances for the national holidays of my country, everything is fine with that, the point is that my partner chose a friend of hers or acquaintance as she says for the dance (the reason why she and I can't dance is because we are from different grades). Then she said that she usually gets along badly with him and that he is just an acquaintance, and she told me that to rehearse the dance better, her friend was going to go to my partner's house to be able to rehearse and practice the dance, and another thing that my partner had told me is that she was very flirtatious in the dance, that she was like that by nature. I don't know, I've already talked to you about it but I still feel that there is something strange and my intuition says so. So to the main question: Am I being too jealous? Is there something strange? I'm not much for venting but I really need answers, thanks for reading.