T thought I was wrong. That this was a woman who hadn't meant to cause me trouble
This was a woman who was a casual friend, at best, who was using you as a cover to cheat on her husband (who had rage problems), while telling you she was separated, and going on double dates with you and your BF with her affair partner.
This woman deliberately
caused you trouble, and deliberately
set you up to be in the middle of a very troubled marriage. She is directly responsible for setting you up to be the target of her husband's rage. So yes, I would have cut her off - I'd have cut her off for using me as a cover for her affair, even without the added drama.
In a more general sense - I don't think that it's possible to maintain a regular friendship with someone who is still with a spouse that has threatened you to the point that you needed to have the police involved. It's like sneaking around trying to have an affair with someone who has a jealous, violent husband, except you're not even getting any Scrabble out of it - the risk of them finding out and targeting you is too great. And I don't agree with your BF - you were right to be scared of her husband. Anyone who requires police intervention to stop threatening you is not safe.
In general, the best you can do when it's apparent that your friend is in an abusive relationship
, is to try to maintain a fairly tenuous connection (meeting for coffee occasionally in a public place, a phone call from an unlisted number) in order to, basically, be there to offer support if they decide to leave.
In those situations, though, you have to be willing to accept the frustration of being friends with someone who is choosing to stay in a bad situation, knowing you can't fix it, and nothing will change until *they* decide to do something.