My close friend is backstabbing me. help?

so i met this girl through my best friend. Trust me , my first impressions of this girl was unbelievable :/ she seemed like a LOVELY kind hearted beautiful girl that always comforted me when i needed someone. I actually had so much love for this girl whom i took as my own sister.She would leave me messages telling me that im gorgeous, she loves me, she misses me, all us friends need to meet up etc... basically to sum it up, she`d do all that sweet talking?! lol ive known this girl for over two years, we`ve been close friends ever since! However, as years past, i gradually realised that she was backstabbing me, gossiping about me behind my back, creating UNBELIEVABLE Disgusting rumours about me and my boyfriend, including her own friends (which have also realised now what sort of hypocrite she is). Shes being ever so two faced, she shows me that she actually gives a ****, being that "almost perfect" friends you could ever have, then behind your back, being utterly b****y. yes i was frustrated, but i guess it left me hurt. Shes doing the same to other girls. And its clearly ironik for me. I know what her game is but she doesnt know that i know ! LOL, im not looking to take any actions just yet, but once my exams are done i shall confront her. I dont want any arguements because lifes too short right? if i were a dramaqueen id approach her in public and create a scene. Also, her actions have built up which actually make me and my friends suspicious on some issues. Shes telling her bestfriends family what she gets up to behind her back. So it makes me wonder whether its happenbing to me. It all adds up!!!!!!!! which is so shocking! guys, any help? : xxx