I feel like my friendship is becoming toxic

Hi everyone,

So one of my friends is always trying to get between me and my other friend (let’s just say s) a year ago they used to be best friends but things have changed since then, s is starting to drift away from her because of her behaviour (I’ll tell u what she does in a sec) and how she acts whenever I’m with her so now me and s are best friends and the toxic friend keeps coming between us, say if I’m going somewhere she’ll just invite herself there too. It’s really starting to get on my nerves. She does other little petty things like say if we have an exam and we get lower than her then she’ll laugh and stuff at us but if we get higher than her she’ll get annoyed and say we’re showing off. I recently got 86% on one of my mocks and she got 45%. Rather than congratulating me she just said “you only got a high score because you have a tutor” not to mention the fact that I’m in set three and she’s in set 2 and it’s not my fault she didn’t revise enough. Only three days before the exam she was talking abt how she hasn’t done any revision. But that’s not the point, she’s always mad at me for not reason and ignoring me and stuff. Like yesterday I was literally talking to s abt a hamper I’m gonna buy for her birthday and then she got mad and started ignoring me. Sometimes she gives a reason that I’m always talking to s but then she never gets mad at s even if me and s both do something to annoy her she’s only ever mad at me. I constantly feel like I’m walking on eggshells around her and can’t be myself cuz she’ll just criticise me. I also know that she’s literally been complaining abt me to s (s told me everything she said).

But sometimes I feel like it’s my fault because s and the girl used to be best friends but things have changed since then but I don’t think she gets the hint