I am 24M and my gf is 23F. We dated for 6 months. So we were coming back from a friend's wedding, our city is a 5 hr car ride away. On the way, my gf asked if we could pick up her younger sister from college, which was just an hour from the wedding venue. I was fine with and we reached the college, and my gf just ran out to greet her sister, and they just like hugged and talked for like fifteen minutes while I was waiting in the car. It was kinda awkward and they both were too clingy. My gf got in the car, and she introduced her sister, I politely greeted her, and we were on our way. We still had 4 hrs to reach home. They just kept chatting and chatting, I just felt left out. Then we stopped for lunch, and my gf sat beside her sister, and they talked, they tried to include me, but her sister and I didn't have anything in common to talk about. They kept telling each other inside jokes and all. I found her sister to be too clingy...like no siblings I know are that close with each other. No one talked much on the ride home. I bought this topic for my girlfriend the next day. She got all defensive, saying that that's how they are, and she had to step into the mother role after their mom died when they were kids. That made sense, I guess, but still, they should have tried not to make me feel left out and see others outside their little sister's bubble. My gf stopped texting after that and is just giving me a silent treatment like a small kid. So am I the asshole?