I am not specifically involved with any political women's movement and I am not and never have been married, so I actually don't have a personal part in this.
But let me give you an example of my typical experience as a fellow male.
I was assigned a 4 week travel to Ft Worth TX to evaluate contract proposals with a guy from San Francisco and another from Washington DC, The other 2 guys were married. It took them only 2 days to find "temporary wives". For the 4 weeks. They cheated the instant they possibly could. And they were typical. And that guy from Washington DC was my supervisor. I detested him after that travel. He left the govt soon after, seeking fortune and fame in the commercial world.
I have to draw upon my experience from the 1970s to respond to this, and even then I don't know if it's appropriate because I'm not sure where you were going with this story. I met a feminist woman back then who was all about having sex with multiple partners, including the husbands of her friends (sisters as she called them). Her justification was that this was OK, because all men do it. The fact that she wrecked one friend's marriage was one negative outcome.
First, I don't care how many partners she takes on. If she wants to amass a record, then go for it, and I've known a few women like that. To each their own. But I think her reasoning was wrong. Not all men do that. More likely it was pure and simple lust on her part, but that requires no justification to me. We are all biological beings, but can still make choices.
As far as your colleague's behavior, I've heard that some people have agreed upon open marriages, but I doubt it's the norm, and I question how many marriages are actually that open. If they are, then I'm not going to worry about it.
But infidelity can do a lot of damage to yourself and others, including other people's marriages, and your own, and especially to the partner you have made a commitment to. And infidelity, whether by men or women, seems like a terribly selfish behavior, not withstanding the physical health risks to you, to others, and to the people you presumably love. It's not a very nice way to treat others.