How do i get my friends to not be friends anymore? plzzz help?

ok so i have these 2 friends, my best friend is blair, and my other not so much friend is izzy. me and blair have known eachother for 10 years, we r 12 and all in 6 grade. me and blair have so much history and have been friends forever. and me and izzy have been friends for a while, and blair just came back into my school, and all of a sudden izzy and blair are best friends, and i feel really left out, and me and izzy arent close at all (but i really dont wanna be) and i just think its not fair, because i just want it to be me and blair, not me blair and izzy, can u tell me a way for them to get in a fight for a long time, and please DONT HATE, and dont say im selfish or whatever. just tell me how i can get them to not be friends.