I feel left out by my best friend

I remember she was talking behind my back when i confronted her and she made me feel like i was replaced at first I thought nothing about it but now I feel left out like fuck she now has another best friend who is apparently her cousin but have never met before at first I was like nice congrats but now it hurts to see them be so happy together but when I try to talk to my best friend she doesn't even reply sometimes and I have been dealing with this for a year and I don't wanna do this anymore