Keep what a secret at this time?
The wife already seems to know she loves the friend. The wife already seems to know that she's thinking poly things. The mistake here seemed to be sharing BOTH those pieces of info at once. Rather than one at a time.
I think backing off for a few weeks/months could be beneficial to the OP. Spend some time reassuring the jealous wife so she can "come down" from the emotional high first. Calm down a bit herself because she seems upset.
THEN decide what they want to do next from cooler heads.
I'm not saying she deny/suppress who she is to the unhealthy point where she is self-hating. I'm not saying to avoid talking about it forever.
I just don't think pushing the wife toward talking about undertaking a major Life Change at this time while wife's freaking out
is the best time to be doing it or the best way to be doing it. That is all.