I get it, OP.
Some posters on here can't bear to think of a woman holding another woman accountable for her actions.
A few years ago, my best friend had an affair with a married man and he left his wife for her. I was the only one of our friendship group who knew it started as an affair - everyone else just believed that they'd met at work (that was true).
We remained friends but she was clear about how I felt about it all.
I began to distance myself from her when she complained about his ex wife not wanting her to meet their teenage children, not wanting her to lavish expensive gifts on them and move them into her house because it was nicer and she was nicer than his ex and, "I can give them a much better life than she can."
And then the inevitable happened. He cheated on her and did a midnight flit.
Everyone rallied round to support her, called him all sorts, how could he do this to her, poor her. And I just had enough.
I kept her confidence though and never told anyone it had been an affair but it resulted in me losing the entire friendship group because no one understood how I could be so uncaring.
They hadn't heard the shit I'd heard for 3 years!
And him? Well he wasn't my friend in the first place. I didn't need to cut him off. He tried getting in touch with me about a year after he left her and I ignored him 🙄
You can't cut off someone who isn't your friend in the first place.
But you might well find that your other friends take her side if they don't know why you've done it and feel that you're being unkind to her. You just need to decide what's more important to you.
I made the right choice.