Right and if you read her articles from 2021, 2022, and 2023 the warning signs for the breakdown of her marriage were apparent. Warning signs that she published. Articles about how "polyamory isn't working out for me so well" and "I don't know if this is going to end in my marriage breaking down" - years before her husband caught feelings for someone. They both kept down that path though. Again that doesn't invalidate her pain but it does mean that she did have an active role in the situation developing the way it did.

I mean the reason she became poly to begin with was because she wanted more sex. Not with her husband, but with other people specifically. Her husband wanted more sex with her but she didn't want that, she wanted sex with other people and said to him "you can fuck others as well, so you should be happy with this". Initially she ended up getting all these dates and fucking all these other men and he wasn't getting any dates, and she was like "that's a you problem". Then she fell in love, when the rules they had said not to. And again her husband just was expected to be ok with that.

But now when her husband finds someone and decides to leave her, she feels betrayed?

It's valid to feel betrayed but that is almost certainly how her husband felt about her own previous actions so imo they're even in how they contributed to the breakdown of the marriage together.