Personally I would cut her off, most likely this will have the reverse effect for a while and she will freak out and try to stay involved with you but in time she needs to sort out what is going on in her own house.
I choose to imagine what I would do if I was in the husband's situation (not that I would ever LET it get to this point), but I know I would not want someone like me out there with a grudge, wondering if he was going to square things up. People do some crazy shit for love, is some freaky S&M worth you safety and well being?