<human>: I have a good story about this. So this one girl, we'll call her Derpa, moved to our school two years ago. I was her first and only friend for the first year of her being here. Not very many people liked her (most people still don't now) but I didn't let my other friends talk shit about her and I let her sit with me every day at lunch and invited her to get-togethers.

She made friends with some other girl that I was friends with. Which was great, I was happy for her. Until I noticed that Derpa started to turn my other friend against me to the point where she wouldn't talk to me. I don't know why, I didn't do anything wrong.

Eventually I just forgot about it, everything went back to normal. Derpa made friends through me and fit in. Everything was fine until this year. Derpa was always rude to me. She would always put me down and say I can't do things. I didn't think much of it, I don't get mad or offended very easily. Then she stopped talking to me, started glaring at me and talking behind my back again. I confronted her about it and asked her what was up and why she was being like this. She said "you're a slut and I've been tolerating you for a year. I wasn't really your friend and I don't want to deal with you anymore."

I haven't talked to her or acknowledged her since. She tries to run up and hug me and say things like "omg I love you I love you you're my bestfriend" like nothing ever happened. It's like she forgot that I was the only friend she had for a year, and I was the reason she even had friends. She doesn't have a right to call me a slut, either. The worst I've done is kiss guys that I date. She meets guys online and hooks up with them 3 days later.

Can you condense the text into three sentences or less?
<bot>: This girl back stabbed me and talked behind my back to friends that she wouldn't have if it wasn't for me.