My boyfriend’s best friend - Am I crazy?

I befriended one of my boyfriends closest friends, who is a girl, because at first I felt weird about the fact that they were friends (I know, childish. Bare with me through, I’m only 18..) and she’s a nice girl and everything but sometimes she just oversteps boundaries between us. Some of the things she’d do: example today I was chilling at him house with him and she calls him up asking him to bring food to her house, he told her no because he’s hanging out with me and she just said that I should leave quickly so that he can go over to her house instead. She meant it as a ‘joke’ but I found it really rude and he was confused about the message as well. Another thing, yesterday they went out together and she just kept taking videos of him telling him how pretty he is and posting it on her Snapchat story. Another thing, she added him to her ‘Girls Only’ story on Snapchat. Obviously, this could be my young brain just overreacting , but if you’re a teenage girl too you’ll see how weird this is - especially since she told me herself she adds guys to that private story when she’s crushing on them. She even posted pictures on there today kind of just flaunting her body a bit? I don’t know. I really like her as a friend because I’ve been getting to know her, her being my boyfriend’s friend and all but I feel like she’s disrespecting our relationship. She’s been friends with him for years so obviously it’s like if something was going to happen it WOULD’VE happened, but I feel so weird. I don’t know what to do.