Win back a friend...?

I totally understand how you feel. You feel jealousy because you are responsible for them being friends when it comes down to it, and now they completely turned on you. Sure they still invite you, but it doesn't really mend a broken heart. My advice, of course you've probably heard it before, is to talk to them about it. Since by the looks of it it's hard to deal with them when they are apart because everyone gets jealous of eachother, talk to them at the same time, maybe at school or something. Good luck xx