I believe she told police that she hadn't 'slept' with him since the murders. I really don't think you question is one which can be answered. All any of us do is say what we think -hope- we'd do.
So allegedly, she withdrew her sexual relations from him - but continued to stick with him and party / holiday etc. Until such time as she had a pang of conscience -and decided to 'do her duty' as an informant - which seemed to miraculously coincide with her relationship ending.
She would have been in a bit of a daze hours after the massacre. Bamber had rang her at 5am saying 'a police car is coming to pick you up'. He then told her MM had carried out the massacre ?
She was asked to identify the twins. And did. Bamber was much too busy talking to the police...............
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Living with and only seeing life as unfolding in terms of black or white surely imposes the most enormous strain on those who follow that tenet. As I previously said, unless/until we're faced with a situation, we can only guess what we'd do.
I DO think she knew way more than she told in her story, which was probably as much about saving her own skin as anything else. I DO think there was a point at which Julie tried to "keep all the balls in the air" and as a result, probably did things which have come back to haunt her. I can't begin to imagine what she thought the final outcome was going to be. She had no frame of reference for it. On a scale of 1 to 10, we can apply to her, every adjective/noun we can think of and for a FEW seconds they'll be appropriate. However, I suspect the real descriptives, as for most of us, probably lay around the 4-6 area, as the 20 year old tried to sort out the nightmare her life had become.