Need advice about friend relationship

So my best friend at the moment has been kind of ditching me for this girl that was on our friend group and that girl bullied me for two years and still hates me to this day and there getting really close and I feel like there trying to get really distant from me or something cause suddenly there best friends they have special nick names and handshakes and everything even though this girl still talks about me behind my back and when im walking with them she flicks her her back at me and makes sure I don't stand next to my best friend or so I think

And when I try and tell my friend she just blames me and says well you can't keep saying all this bad stuff about her and you juat have to get to know her and feels like im getting more and more distant from them her everyday and it makes me really sad cause if they ditch me then I just have the people in my class that I just met at the start of the year but are kinda friends with so I honestly don't know what to do and it honestly has been leaving me kind of depressed, so any advice?