Welcome to the forum, Chris and Michelle.
I am never one to tell people to live. I say...get it how you live.
My only question is why poly-fi? What if this woman wants to have a husband or wife of her own in a legal sense? What if she wants to have children--with someone outside of your husband? Will be she allowed to do that, or is that a breaking point?
I am not bashing either of you. Honestly? I could not give a damn what others do with their lives. If it does not impede my life in any way, it matters not. I am not going to lose any sleep, and my heart is going to keep beating. I encourage people to seek happiness and do what they want.
Do not let anyone run you off. These are common questions and concerns. Quite a few people have either been that couple or that woman, and could it be projection from a negative experience? Maybe, or they could be pointing out the error of your ways and trying to give you a perspective that you may not be able to see while in a situation. I call it the blind spot. Often, it helps me to get advice from unbiased people. Do not take it as criticism.
Either way it goes. I wish you luck, Chris and Michelle. I do hope you find what you are looking for, be an active member, make some friends, and even gain some insight. Feel free to even start a blog about your poly meanderings. Best of luck.