u/Cool-Pressure8577

So my LD gf (20) and me (25) have been together for almost 7 months now. Recently she had went on a family vacation and friends. Her brother had invited some friends too. One of them had complimented her several times on the trip and she had told me about it. I didn’t think much of it at the time but now she has recently told they were going to go hangout one on one. It was a day at the mall and feeding ducks. I expressed my feelings about this and said it made me uncomfortable but she insisted I was over thinking and that he has Just simply been nice to her and that she has not a single drop of interest in him. We had a bit of an argument about it and she kept telling me she’s always telling me if she’s gonna see him and what they are doing and that I shouldn’t be worried. She also says she has told him about us before. Now she says the end of the week he has invited her to go see his family in a family dinner. Am I really just insecure and damaged from past relationships? I feel in a way I would NEVER do this to her and she just can’t understand that. Is it truly possible a guy would be doing this with a girl just to be friends? (She has also “asked” him in person if he liked her and he said “no”)