I dont know if my friends are friends that i should keep?

Well at times they can be SUPER mean. to everyone, including me. Its wierd becaue one min im just sittin down and the next one of thems screaming at me for just like saying something. But at times they ca be really nice. But im sick of being yelled at a talked about. Im also good friends with another group of really nice peeps and when i c how nice they are to each other i kind of get jelous that me and my friends arnt like tht. I dont really ever get mad or yell at my friends and i really dont do anything that should make them act like that. I just dont know what to do. We have bbeen friends for a really long time but they hav beem changn.