My (23F) boyfriend?s (26M) bandmate consistently posts ?cozy? pictures of them together and it makes me severely uncomfortable.

Firstly, I?m on mobile so I apologize. Secondly, I never thought that I would come to Dating.mobi, but here I am. Lastly, Iam desperate and driving myself crazy and need someone else?s opinion because I have been bottling this up for way too long. I have been dating this guy for almost 8 months; we?ve known each other for 7 years and finally got together. This is my longest relationship to date. My boyfriend is a musician and plays in a few bands, one particularly a lot. There is a girl in his band (18F) who has had a notable thing for him (and no, it?s not just me thinking it; it is blatantly obvious that she has feelings towards him and other band mates see it) who has been doing something that absolutely drives me nuts. She has been posting on Instagram selfies and pictures of them consistently. It may have been from before my boyfriend and I even started dating, but she takes pictures of him a lot and will post them. He doesn?t know because he does not have an Instagram. On Facebook, she will post pictures but not tag him in it (maybe so my/his family will not see the pictures and question him about it?).
The fact of the matter is, in the pictures, they are close. The most recent one posted, my boyfriend is actually holding her in his arms. I know it was taken before we started dating (or at least I hope! ?) but I don?t know what to make of it. I have expressed my discomfort to my boyfriend about the pictures. He has tried to talk to her about not posting them but she throws a fit about it (says she might quit the band, stop playing shows, absolutely stop talking, etc.). Another bandmate has spoken to her as well but she continues to do this. They are afraid to make her mad because they have an important competition coming up at the end of the month and they don?t want anything negative to happen before then. My whole point, is why does my boyfriend have to pose in pictures/selfies with her? I know they are in a band together and spend a lot of time together. I am a very private person and I don?t even post many pictures of us together!
I don?t know what my next course of action to take should be. I am ready to talk to her directly. I have shown my family the pictures and they are appalled. I talked to my boyfriend about it, and he said that he took care of it already but obviously not if the pictures keep getting posted. I?m absolutely sick over it. Yet, we make plans to see each other all the time and I feel like our relationship was actually beginning to get somewhere.
Am I overreacting? Am I being petty? Should I speak to her directly? Should I wait and see? Would you be mad if someone was posting pictures with your SO all the time? I don?t know how to rationalize it at all.
Any help or insight is appreciated.
Tldr: My boyfriend?s bandmate posts cozy selfies of them on social media together and I don?t know what to make of it.


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