We have had discussions before, that sometimes grew a little heated, about whether polyamory is more of a thing you ARE (like an identity thing) or a thing you DO (a lifestyle thing.) Some people get upset at it being considered a lifestyle, because for them, it's an identity.
For me, the ultimate freedom is in being able to define myself in whatever ways make the most sense to me as I evolve through life. Poly is a little of both for me...something I am easy with and capable of, yet not so MUCH of an identity thing that I NEED it. For me, it was probably more of a lifestyle. When it became too stressful to try and find enough time and energy for everyone I had in my life, I reevaluated and decided I'd be happier doing something that is closer to monogamy. Yet still, it is not totally like other monogamy that I have done, and seen. My former poly partners are like family to me and I won't be changing that. My mono partner does not control me in my love for other people, he understands that it's how I'm wired and he can trust me. He asked for a certain degree of sexual fidelity, and that is not a problem for me to give. But he knows that asking me not to hug, kiss, or flirt, with people just would not fly. He knows that I have "feelings" for others, and that it doesn't diminish my feelings for him in the slightest. I just don't have sex with them anymore, and I make him the highest priority for my time and my plans.
We are not married, but I would be happy to marry him one day if he wants to. And I've told him this. We are ecstatically happy with one another, almost insufferably so, and we have been for about a year and a half now, with no end in sight as far as I'm concerned. We are that couple always touching, always looking into each other's eyes, always all over each other. And I don't feel like I am missing anything in my love life. He fulfills my needs very well. I "went mono" with him in July of last year.
Will I be happy forever with one sexual partner? I don't know. I'm happy right now.
I think that expecting a partner to treat you in ways that are honest, loving, and respectful, is reasonable. Expecting them to never change or need anything you don't provide, maybe not. And expecting a partner to understand if you are not happy about their choices or needs, or have difficult feelings about them, is reasonable. Asking for compromise is reasonable. Even saying, "I don't think that I can continue in a relationship if you need it to change shape in this way" is reasonable. Going berserk and shouting and throwing things because someone has upset you with a truth you don't like, not so reasonable. Controlling behaviors, not so reasonable.
There were many things I found toxic about my not-happy, long faithful mono marriage, when I was in it, and that I've observed in "normal" monogamous relationships my entire life. Poly or not, my philosophy on relating has forever changed. If anything...poly has made it MORE LIKELY that any relationship I undertake from now on, will have better odds of happiness, and longevity if that is the desired outcome, because I have learned many things about myself and relationships.