Wow do I get what you mean about the theory vs the practice. To different parts of the brain used in these cases.
Likely you will go through a mourning period ....mourning the loss of what your marriage was (or what you thought your marriage was and what it meant ) this takes time and that furniture might have to be rearranged a few more times before its over.
It's great that you talked a lot and are grown ups ...it's just really hard to unring bells. Reading the different stories could give each of you an idea of what to look forward to. Also knowing that she would/will have problems if roles are reversed is something big that she needs to work on. Plenty of stories of one partner pushing for this then melting down when the reluctant partner finds a partner....then they want to throw in the towel go back to being monogamous...tooo late. My wife had a melt down when I stopped wearing my wedding ring.
I agree with Kevin never say never
...again a little reading and you'll see many who came saying the exact same thing and then over time opening up to trying it for themselves.
The spill over effect might require more furniture rearrangement depending on patterns and history of your relationship.....and it's not a given....don't expect it.