I think you are probably the only person her husband slept with that she actually knows, so you're getting the brunt of all the people he's messed about with.
You made a mistake, you feel remorse, you are sorry. Ok, you screwed up, but so did he! To me, I think this isn't your problem, it's hers. It's not your fault he's slept with other people as well.
I don't know how you can get her off your back. Solicitor? Restraining order? That way you can keep it more private than reporting her to police.

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