Am I Overreacting?

Is this appropriate?

Girlfriend of 5 months. She stays in contact with her in laws for her kids, but the ex brother in law hugged her tight in front of me multiple times and kissed her forhead multiple times too, loud kisses, She could tell I didn't like it and talked about it, she says she knows them for 15 years and they're like brother and sister, she was sick so he was worry. Her daughter didn't seem to mind. I told her I'm not accusing her of anything but I am uncomfortable. Now I'm the crazy guy jumping to conclusions to her I guess. i can't help being jealous and mad. First tme I see him. She told me before that after she divorced, he took her to a concert and sometimes she would mention him, I pay no mind unti now I see them doing that.