My best friend has a new best friend?

So me and my best friend have friends since we were 5, and we have always been inseparable, we're so similar. However, this new girl who just moved to our school and her have become really close. My best friend tries to include me sometimes but when were together she ALWAYS talks about Abi and when they're together they laugh about everything. Abi is my friend too but i feel like she's stealing my bf from me, e.g me and my bf have personal jokes and now Abi's joined in and she acts like they're just hers and my bfs. I just feel left out and I can tell that my bf tries to include me but sometimes she makes me feel unwanted. However, she hates it when I hang out with other people, I can tell. Of course I don't mind her having other friends but i don't want to lose her. Should I spend some times with other friends or carry on feeling like a spare part? Thanks :)