I'm a 26-year-old man and I often feel left out of my girlfriend's social circles.

I'll try to be brief. We're both 26 and have been together for over a year, living together and having met each other's families and friends. She studies in my city. Whenever I'm with my girlfriend, I often feel overlooked. She has several social circles spread across different cities, and this dynamic seems consistent in all of them, whether it’s her family, friends, or relatives. They laugh and chat without me while I find myself sitting quietly off to the side, waiting to go home. While there are some friends of hers I connect with well and a few situations that feel normal, about 95% of the time, I feel excluded. This is unique to her and her groups. I'm an extrovert and generally sociable, easily making friends in various environments and cultures. I've navigated countless social settings and have never encountered this issue before, yet it persists with her friends, who also come from diverse backgrounds. Lately, she’s been distant and even labels me as antisocial. I’ve tried discussing my feelings with her, but she often brushes me off and doesn’t take steps to improve things. I engage in conversations, share opinions and jokes, but it feels as though no one pays attention. It’s disheartening that neither her friends nor she makes an effort to include me, even after I’ve expressed my feelings. When we are alone, her attitude shifts, as if I’m a backup option for her. This has been the case since we first met her social circles. My family noticed a lack of respect when our families met; it was just a brief exchange before everyone went back to their groups, leaving us in uncomfortable silence. This pattern isn’t limited to her family; it occurs with many of her friends from various places, even those who don’t know each other. I’ve no reason to think they dislike me, and she claims her family appreciates me. For instance, this week we visited a restaurant with some of her old friends, many of whom I know. For two hours, they reminisced about high school while I and a close friend of hers barely managed to say two words. My girlfriend was engrossed in conversation with her sister and a high school friend, frequently turning her back to me at the table. Despite her sister’s behavior, my girlfriend stopped mentioning it. I attempted to join their discussions about shared memories, but they just smiled politely before returning to their chat. When the topic shifted to politics—something I’m knowledgeable about—I tried to contribute, but they continued talking over me. Later, my girlfriend seemed upset that I wasn’t more involved. I told her that, despite my attempts, no one made the effort to include me, so I didn’t feel engaged. She didn’t accept that, so I shifted the topic by mentioning I was hungry. This encapsulates many similar experiences I’ve had repeatedly over the past year. I’m seeking advice—am I at fault, is it her fault, both of us, or something entirely different? In short, I feel invisible around my girlfriend's family, friends, coworkers, and relatives, a stark contrast to how I interact with other groups where she isn’t present. I have no reason to believe they dislike me, and I genuinely make an effort to be myself. What’s going on?