Your not over reacting. My guy wold shit a brick if I just left. He's ALWAYS with me as it is. He's like my best friend so were always side by side. We never leave without telling each other, hell he tells me where he's going when he's going outside to smoke a cig. I think that the proper thing for her to do would have been to tell you and/or ask if you would like to come also. I know its weird but I don't think ive been alone since we started dating 2 years ago (except for one or two rare times)