I think my girlfriend likes my best friend more than me,how do I bring it up to her that it bothers me?

Me 19M and my girlfriend 19F have been together now for over a year. Everything’s been going smoothly until now. For some context we have a really close friend group consisting of five people and my girlfriend’s been part of it,we started dating from being friends too. So in the last couple of weeks things have been off with my girlfriend. I tried to not take it seriously because sometimes things just happen but lately I started noticing that she’s been hanging out with my best friend an awful lot lately,which I didn’t mind I was happy they were getting along,until my girlfriend started acting strange.Before she hung out with my best friend she used to tell me how much she loves me,she also used to send cute videos,and always complain how much she missed me,things like that. But after she started hanging out with my best friend she hadn’t been doing any of that which was strange but I brushed it off,until she started acting much stranger. She started ignoring me and sometimes downright dismissing what I say. A few days ago the entire friend group decided to go to a theatre,we all arrived there bought our snacks and sat down. My girlfriend hesitated to sit down just when I was about to ask what’s up she sat down next to my best friend instead of me which was strange but alright I guess. Throughout the movie my best friend and my girlfriend laughed at every little thing and touching each other an awful lot. After the movie I asked her about it,which she again dismissed. How do I bring it up that it bothers me that she seems to like my best friend more than me or am I just overthinking it?

TL;DR My girlfriend acts as if she likes my best friend more than me and it really bothers me,how do I bring this up to her?