should I stay with her and try and put things right or walk away?

I'm looking for abit of relationship advice. In a nutshell this girl who I am in a relationship with, well kinda anyway, have been through alot in the last 8 months. We went from being engaged to just being gf and bf because I left her when she had a broken foot which yes I felt very guilty for. Anyway we made up and got on with things, she and her friend got arrested for attempted murder which apparently was my fault even though it was my parents who made the allegations but I'm guilty by association. Fast forward a wee bit, we have argued yes but nothing more than usual and we just got past it and got on with our relationship. Recently I went to pick her friend up from burnley which if you take into consideration I live in harlow, it is quite some trek there and back not to mention fuel. Thats when things started to go bad, she started saying that I must do this and starting shouting and today she apparently informed the police that I stole her CD's that she left in my car, no truth in this as I haven't taken anything from her. It aint my fault that she left cd's in my car and now they are gone. Now she wants 100 from me to replace them or she's going to get an injunction out against me?! To top it off she is treating this guy (the one I picked up from burnley) like they are an item, but she claims otherwise. Even to the point of sleeping with him and not me! She constantly says do this or f*** you and i fool for it like a lovesick fool. What should i do?