Please help me ! :(?

I have been really stressed for weeks now and it is really starting to annoy me. I know I shouldn't be acting like this, but I don't know why I am. So basically, I was in a group of four friends (we were all friends but had a best friend in the group aswell) until me and the girl I used to be best friends with had an argument and drifted apart. This split the group in two and made us swap best friends .. my best friend now is (we will call) X and the one she used to be best friends with is Y, who took my old best friends side and followed her to be popular �� . So everything went fine and I was really starting to like my life with my new best friend and thought nothing could ever go wrong.. until Y got pushed away from my old best friend and started to crawl back slowly. After a while I thought I had nothing to worry about and that X wouldnt be stupid enought to let her back.. Then Y started to pester X and would constantly bug her.. but my best friend X didnt mind and started to be friends with her again. I knew what she was trying to do and (what I now regret doing) put facebook statuses about it secretly.. After they both read it and understood that it was about them, left me stranded at school to be compeletly on my own.. I apologised for doing this and was forgiven by X and she told me that she never meant to push me out.. However the next day she left me on my own and I panicked and went home faking to be ill.. The following day I thought that I should be stronger and went into school with my head held high and went on my own at break etc. But I then had Math with her and she came in looking suprised and asked me where I had been.. we then got on laughing and joking around during the lesson and ate lunch with her.. Since then it has been fine and we have got on and gone together at school.. Now, onto the problem.. I keep panicking on the fact that Y could come back and they could go off together as they did before and I constantly dread going to school as they are still friends and chat and stuff. Y is not on her own or left stranded and has many friends to eat lunch with and go together during cl.. I have tried to see if we could get on and talk to her but she just gives short answers and almost ignores me sometimes with just nods etc. If I was left on my own I would have people to eat lunch with, but in my cl people have their best friends and I get on with them but they all are pretty intimidating and nasty to each other and I just dont want to get involved in that. I am constantly looking for warning signs of my best friend, X for not liking me.. Sometimes she goes blank on me and says comments and I panic that she is going to just get up and leave me like she did before. I know that it must seem stupid that I am stressing about something as silly as this, but I just need some advice! Thanks