Dating

Concerning friendship between boyfriend and his female best friend?

My boyfriend and I have been together for seven months. In the beginning of our relationship, I met his friends and in particular his female best friend of 4 to 5 years. She seemed nice and I didn't have a problem until I've seen certain red flags as the relationship has progressed. First and foremost, I want to emphasis that I respect his friendship with her and I wouldn't expect her to stop being friends with her. I have male friends too and that would be hypocritical. Firstly only after six months in the relationship did he want to post me and him on instagram BUT yet his Instagram profile is plastered of photos of him and her. [further detail in another question] Secondly she has once sent pictures of herself in a bikini bottom showing her legs and stomach saying she is 'burnt' Lastly we went to a birthday party and during the night whilst I was talking to friends, she was wrapping her arms around his neck and putting her head on his chest for a while of a night whilst they were engaging in mutual conversation with their friends and I was right next to them. She has a boyfriend and I feel as yes, it's my boyfriends position to place boundaries but it's also her position to respect me as his girlfriend. I've spoken to my boyfriend but he says she's just a friend and like a sister. I don't know what to do, give me some advice?
Concerning friendship between boyfriend and his female best friend?
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