In a parallel world, I am the husband.
My wife and mother of two kids has told me she is interested in other guys.
It was/is rough. The roadblock is that:
1) You are asking him to rewrite his worldview
2) You are asking him to renegotiate his marriage contract
You can try to make it easier by doing one without the other; it was hard for me because my wife was trying to do both at once, but became a whole lot easier to deal with when we talked it out and came to this conclusion:
1) My wife has agency; if she wanted to cheat, she always has that option. It is better instead that she is honest and open and fair.
2) Because there is agency, there is no 'rush'. She felt there was a deadline pressure or the window would close. There is still tension because I'm still rewriting my worldview, but at least our marriage contract is still stable-the same- until something happens.
#1 is as simple as saying, I think, "I fancy Guy Fellow at work." He is a man, and likely has his own list of women he thinks attractive. Start on common ground.
Note that I don't have a better answer because I'm still writing that chapter of the book! My wife went on a couple dates (that I probably wasn't really ready for!) and slowed down after talking to me, but also because the holidays is a really busy and stressful time for everyone. She is still getting messages from the guys, and still tells me about them, but hasn't made any effort to organize additional dates at this time.
The hardest part may be how your time is spent with your husband. Do you literally do everything together?