I was at university. Had a group of four girls all living together from the first day and I made friends with her and brought her into the group as I felt sorry for her as she hadn't yet made friends (warning sign anyone???)
She was hilarious and wonderful and everyone liked her apart from one girl who thought she was a bit off sometimes. We were best friends and I was so happy to have brought her into the group. after about six months she suddenly went a bit weird with me and her and another girl from the group started doing a lot of stuff together.
It wasn't a big deal because we were all friends but then I got left out of shopping a couple of times and then a night out, and I got a bit upset as in a group she would talk over me and ignore me etc.
I thought I was being pathetic until she started saying things which weren't what she has previously told me (that makes me sound petty but things like that she had been travelling, lost virginity to a pop star, been in music video, been abused by parents) and I challenged a couple of things, and she fell out with me saying I was jealous. (Which I probably was) it was at this point the girl who told me she was off said that was what she was like with her all the time.
then we lived together with some other girls in the second year and she did exactly the same thing to another girl so there were two of us wondering what happened.
By the third year I was bored of it and moved out of the house and lived with different friends but her behaviour escalated to the point that no one knew where they stood but everyone was frightened of upsetting her.
She did a couple of really horrible things like pretending she had taken an overdose the night before some exams which my friends then spent overnight in a and e and unsurprisingly didn't do as well as they could have, and Pretending she was pregnant etc.
Even though they all saw through her too, I think they were just all a bit more forgiving of her and they all stayed in touch after university. I avoided anything where I knew she would be but bit by bit just moved away from being friends with them.
I don't miss them as I had a group of friends from home and other great friends from universoty but I still feel responsible fifteen years later for introducing that PSYCHO into our group.