Don't blame yourself for supposedly 'triggering' the series of events, obviously the issue runs deeper than that. It's not your fault. Obviously if you guys had been able to talk about it properly, things would have been different, but it seems that she's pretty mental.
EDIT: Personally I think it's ok for people to hang around with their ex-s. I mean, if everyone can be mature about it then I don't see why people have to stop being friends. It's all about trust.
