HELP!!! My friend is stealing my other friend from me!?

Me and my friends are like super close! I love them and they love me!!!! But my friend, lets call her Katherine is stealing my best friend lets call her Jasmine. Jasmine has just moved here and i really like hanging out with her! Katherine thinks i'm stealing Jasmine from her but i'm not! Im just hanging out with her! And whenever i see Katherine lonely i ask her to join us but then she just ignores me. All 3 of us use Facebook so we can chat with each other. Well when ever i post something to tell Jasmine something she just butts in! Katherine is also always correcting me and she thinks she's all that! You can say that were all kinda nerdy but Katherine is like so annoying! Sometimes I wish Jasmine can see it but she's super nice to realize how Mean and annoying Katherine can get!