What do you consider appropriate for your ltr when going out in mixed groups together?

For example, my ltr is extroverted.

Last weekend we went out to dinner with her friends because it was her girl friend’s birthday. There were two couples, us and another (the girl and her boyfriend, average but confident) and two other girls. Ltr talked with everyone but mostly with him. She laughed when she saw him looking at some bread in a funny way so she gave it to him. After dinner we went to their home, eat cake and played some logical table games. At some point my ltr said to another girl “take this thing” and he made a joke along the lines of “this thing sound like something else” at which she replied “stupid” while making a slight smile/giggle. The thing that pissed me off is that she said “stupid” in a similar, if not the same way she uses to say it to me (kinda sweet way)

I found it disrespectful. I confronted her (mistake) but I wanted to know if she was into him. Cause I’m starting to have enough. She said no and she didn’t know why she said those things in the same way she says it to me and that she realized what she said only after, and that made her sad. She apologized. Also she affirmed that she smiled at that joke because she didn’t want to ruin the night for everyone.

I’m her first serious relationship, she has lots of green flags. The only red flag is that she has three guy friends.

I made it clear that relationship means trust and mutual respect. Without those there is no ltr. Yesterday she brought me lunch.

What do you think? Is this disrespect or just my insane insecurity speaking? Or is she’s only being a kind extroverted? The only thing I know is that I’m running out of patience and considering to break up with her.