Is it my fault that I lost my best friend?

This girl and I were best friends for 8 years. We were in a friend group of 5 girls. One of the girls moved schools so we don’t see her much but the rest of us still attend the same school. One of the girls in the group(lets call her B) told me she didn’t like me, but I already knew that cause she would constantly treat me like shit. I decided to leave the friend group because of her. My best friend understood why. This happened in 9th grade.. fast forward to 10th grade, i tried being friends with B again but she would constantly say shady things. My best friend wouldn’t talk to me around B and would ignore me. I found a new group of friends now my best friend and I have completely stopped talking. She chose B’s side over me, she would hear the shady mean things B would say to me but she still stayed friends with her and ignored me. Is this all my fault??