Not everyone who is poly feels this undying need to be poly. There are people who can happily navigate monogamy while being polyamorous.
I am not sure I would be willing to lose my wife over my need to have other partners. I have never been forced into that kind of decision, thankfully, so I can only guess at what I would do.
I guess it depends on how poly you are. Mny moons ago a group on this forum made a sliding scale of polyness. It was close to the Kinsey scale.
1 - is capable of loving more than one but neither craves it or looks for it. Is a possibility without expectation or requirement
3 - enjoys being poly, dates, hangs out, can love more than one, but can take or leave it as well. Can go years seemingly monogamous and then find someone to enjoy being with.
6 - can't fight it, craves it, wants it and can't live any other way
Maybe you need to decide what poly means to you, where it fits in your life and then... What does your primary relationship mean to you?