Guys, how close should a best friend be?

I’d really appreciate some male perspective on this. So last December I reconnected with a guy I used to date. Since then, we’ve been on and off, majorly because I’m not sure how to feel about one of his best friends (a girl). They’ve both gone out of their way to let me know that nothing has happened between them (I never ask) so that’s reassuring. On the other hand, their dynamic is just odd. When we go out and she’s drunk, it’s like she wants all of his attention on her. She constantly calls him over to wherever she wanders off, when he’s clearly spending time with me, and just overall seems upset when he stops tending to her. For his birthday this year, I wanted to spend time with him, and he said he could after dinner with his “family”. Come to find out it was at her house, and he wanted to come over with me at around 11p. Of course I declined. Moral of the story is, he prioritizes her more than I’ve ever seen a guy do with a friend, to the point where it’s uncomfortable. I’m having a hard time because according to him he wants to be with me in the long run and is in love with me, and he expresses that in front of her, so I’m no secret. I don't know, Should I be bothered? Will this blow over? Thanks so much in advance.
Guys, how close should a best friend be?
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