My friend's sooo bitchy?

[Alix P]

At first there was this two, me and my friend ami. Then I introduced a new friend Tiff. Then ami and tiff went shopping and I was fine with it until when I invited Ami for a sleepover and TIff went a bit funny over it. On the sleepover, Ami told me that when she and Tiff went shopping, Tiff bitched about me to Ami all day and how annoying I was. So on bebo I confronted Tiff and we had a big argument. The next day I went into school with Ami and Tiff was all dazed and hung out with a really unpopular group instead of our big group. At the weekend we had another argument but Tiff said some really horrible stuff, like swearing at me and i was a bit horrible back and did some screen shots to show Ami, however, she didn't turn up for school because she was ill. Soon our group had seen it and Tiff read it because she wanted to see the bit of paper, and she stormed off. Everyone was on my side until she came back and burst into tears. Now everyone's against me because of her. What should I do