I agree @MotherofGorgons . I think some people of every new generation (OP sounds very young and has no idea that this isn't anything new) start out by reinventing open relationships and usually end up monogamous. Like democracy, monogamy is an imperfect system that leads to a lot of frustration and unfairness but seems, on the whole, to work better than the other available options.
I have a friend whose parents had an open marriage from the 1960s to when they died only a few years ago. One of them was a well-known public figure in the 1970s and 80s and their open relationship was widely known. One of their large family of children was the offspring of one of the mother's lovers and sadly was never fully accepted by the husband. I knew several of the children when we were growing up (we lived in the same area) and I'd now say that the older ones suffered because of emotional tensions and the fact that their parents were busy managing their relationships with various partners. The marriage was one of those tempestuous ones — a bit Taylor and Burton. My parents were so very dull and boring by comparison. The older kids had to do a lot of parenting and carry a lot of responsibility while their parents were off doing their thing. I was spared that. One child committed suicide in his late 20s. Another has spent long periods in and out of psychiatric institutions.
They are one of those families that look impressive from the outside — both parents widely admired in their field, the mother in particular held up as a feminist heroine — while the reality (major MH and psychological issues among the children) isn't talked about. Once the children had left home, both parents went off and lived their own lives. Then when they got into their 70s and 80s they wanted the children to support them and leaned on them very heavily. I oscillate between admiring the parents for being self-focussed enough to do what they wanted in life and thinking what selfish, privileged people they were.
Class plays a massive role in how this kind of relationship set-up is perceived. Being polyamorous or whatever people care to call it when you're working class and living on benefits is one thing: being polyamorous if you're a minor member of the aristocracy, where you marry for pedigree and to conserve the family fortune and infidelity is taken as read, is another.
As a feminist and a woman who believes that women should have the freedom to live their lives as they please, including defying social norms, I struggle with the idea of monogamy. I also struggle with the idea of bringing children into a set-up where the children aren't the centre of their parents' lives.
Mary Harrington is a feminist who used to be very libertarian but now writes about these issues. She has come to a position, having been in OP's shoes, where she advocates marriage and monogamy:
https://reactionaryfeminist.substack.com/about
Here she is on You Tube raising a lot of questions that merit consideration:
I think it's important feminists talk about these things.