I was in a monogamous marriage 19 years. It ended for reasons that have nothing to do with cheating or monogamy, but now that I’m out; goodbye monogamy!
I was in fact very faithful to my ex husband, but now that I am divorced I have embraced polyamory and I love it.

I’m only in lesbian relationships these days, so whose cheating, man or
woman isn’t relevant.
Personally I have found the opposite of what people expect with polyamory and what you are writing about. For me, It does feel like I am “settling down” and poly feels very supportive of that.
I recently became a mom and had a baby. My girlfriend and I live together and she is so happy to be a Mom with me. She has other partners, and recently I met them and they are wonderfully supportive of us as people and parents. In fact poly really helped us in being parents because she had more people to lean on for support and community which we badly need as new parents. Having just given birth, I have no desire right now to date anyone or even have sex-so I’m not planning on dating anyone else myself right now. But I know eventually if I feel bored or fall in love with someone it’s okay and I can be with them. I can’t tell you secure that makes me feel in my relationship. Also, since I just had a baby and don’t want much sex, I love knowing that my partner has other lovers she can have sex with right now. This has made things so much easier for me.
I wouldn’t say monogamy is dead, many people still want it and are happy with it. But I like the idea of people like me being more accepted. People deserve to have choices, and for me it’s just much easier to settle down into polyamory. My parents and family don’t even known I’m poly as I don’t think they can handle it or understand how well it works for me and my girlfriend. Options are good for people, let’s have more options than just monogamy.