Becoming Poly is more of a life journey or a process rather than a moment in time. The big challenge for most is a basal change in thinking that has been conditioned into us since the day we were born and those changes don't come easy or without conflicts. One of the most basic changes imho is to begin thinking in terms of "we" instead of "I" or "you".
"After what feels like careful thinking, several conversations later, I've decided I think I'd like to try poly. I'm not sure what happens now but....I'm trying it I guess! Right now it just feels like I mean "Hey, partner, I don't want you to feel miserable! Please, do what you need to feel a happy full life".
Now insert the plural instead of the singular in your above comment. There, now you have begun the Poly journey.