It's hard to believe you're that obtuse to the difficulties in actually prosecuting sexual assault Chris.
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So the audio recording wouldn't be sufficient because it doesn't provide evidence that he did, rather than talked about, raping her. That's the burden of proof that "she" would have to provide, which a reasonable man might accept is pretty bloody hard to do. I suspect many look to the fact that she has gone to the effort to record this as saying it's far from the first time to feel confident that he is a nasty piece of work.
Similarly, it's pretty common for victims of abuse to stay with their abuser (
https://ncadv.org/why-do-victims-stay), which as a teacher who presumably went through safeguarding training I'm staggered you aren't aware of. Yet you continue to take the side of the man. It's grim to read.