(I know her really well), but that's not my place.
It's not your place to press honesty, integrity and ethical behavior?
But it is your place to enable lying and cheating?
You are having an affair. You are disrespecting and mistreating this woman.
Cheating is not polyamory.
Feel free to read my story for frame of reference regarding what personal experience I base my assertations on.
So long as you are allowing yourself to participate in unethical, deceitful behavior-you are not ready to explore polyamory. That goes for him as well.