My girlfriend and I (both early 20s) have been together for 6 years. We love each other very much and we work on our relationship actively. She's straight. One of her best friends is a straight and single male, and they've known each other for 8 years. Her mother recently passed away and life has been very tough for her. I'm being there for her in every way I can and as much as I could. However, I understand that I can't be her everything all the time and she needs to spend time with her friends and family to also help her with her grief. She let me know that she wants to sleep over at her male/straight/single best friend's apartment an hour away from where we live. She also told me they would play with play doh and video games and then she'd sleep in a different room. Since I thought it'd make her feel good, I didn't object at all and told her to have fun but not to do anything over the top, as she knows. The night she goes, she texts me that she forgot the play doh and they're instead watching movies and that she's "a little drunk". I'm very upset at her because I felt disrespected that she put her self in a compromising situation with another guy. She tells me she's an adult and she didn't do anything with him because he's just her best friend. I still can't shake off that feeling of weakness and disrespect. I want to know what other people would've felt. With just this situation, am I being overly jealous or the right amount? If I'm wrong and being unreasonable, I'm more than happy to go apologize to her.
Anyone would be mad about that, and she had no business doing such a „sleepover“ if she‘s in a relationship. .