I'm being blamed.

I feel I should give some background information about this, but please don’t be put off by the length of it :) Okay, so I’ve been best friends with this girl for about a year. We never really knew each other before college but we’ve both been drawn towards eachother through similar experiences (we’ve both been let down by our friends when we needed them most, both have long-term problems with our mental health). A few weeks ago we both decided to go to the doctors about depression and such, and we were both put on antidepressants. The things is, she told me she was “diagnosed” as bipolar, when she only went to the doctors once (I had a year off school with depression, saw the psychiatrist twice a week and I’ve never been diagnosed with anything). So I know she’s lying. Also, she wouldn’t be put on antidepressants as they could cause her to become manic. I really don’t understand why she would WANT to be bipolar, and I think it’s insulting to those who ACTUALLY suffer with the condition. She tells me little lies all the time, and I just brush it off, but with this I feel she’s gone too far. It seems like any time I confide in her something about myself she always has to come back with something worse, as if it’s a competition. Well, today she told me our english teacher said to her that our bond is not good for her, and being around me makes her depressed. This made me feel so horrible, as if it’s all my fault, when actually she brings me down quite a lot. Also, he’s been my teacher for my entire time at school, and he didn’t say the same to me, so I feel like he’s stabbed me in the back and told her to sabotage my feelings to save herself (and it’s not like it’s because she’s better than me academically - I was a consistent A student before I got ill, and I’m working at bringing my work back up to that level). Needless to say I felt like sht, so I locked myself in the toilet and, I’m disgusted to say, cut myself again. The thing is she asked me to come out, but she was the last person I wanted to talk to, then she started crying to everyone like me being upset was only a problem because she was upset now. Anyway, I just fancy an outsider’s perspective on my situation, so I’d be so grateful if anyone could help me. Thankyou in advance x