Boyfriends Best Friend Is A Girl

I’ve been feeling really insecure lately. I’m already an insecure person to begin with but my boyfriend and I are in a long distance relationship. And he has a best friend back home who happens to be female and it just makes me uncomfortable. I’ve seen her on Snapchat and she’s pretty. And they’re always doing things together(always with another mutual friend) never alone. But it makes me feel even more insecure. I don’t know how their friendship is because I’ve never been around them together. I don’t know if she has feelings for him or if he flirts with her. I know it seems like I don’t trust him, I do. It’s just my insecurities really get the best of me sometimes..