What are best practices in engineering bounds likely to ensure that a friendship doesn’t endanger a marriage?
I feel like this was originally given no context, then you say this would be with your AP.
You can have a friendship with your AP, but you will never reconcile. You can choose your marriage by going completely no contact, or you can pretty well expect to divorce. Keeping contact with her will likely lead to reengaging in the affair, and it will devour any chance you have of creating the security your wife needs to heal.
What signs or timelines guide when a marriage has healed enough to accommodate an extramarital opposite-sex friendship?
I think you need to decide if you want to prioritize your marriage or not. If you do, then you will not be worried about when you can have female friends again. This is a natural consequence of cheating. You have destroyed any stability, security, safety, feelings of specialness to your wife. It takes a long concerted effort to rebuild these things for your marriage to even have a chance at survival. If you are unwilling to do that, you are better to leave now rather than torture her through a half assed effort. After an affair you have to be all in, there is no other way it will work.
Is the permanent sacrifice of a deeply meaningful extramarital friendship with one’s affair partner justified by emotional necessity for the betrayed spouse?
Unequivocally yes. Also for you. As long as she remains in your life you will resume the affair. And even if that is not your intention, it will happen.
Affairs are rooted in feelings creqt e by the affair itself moreso than any AP. I know that doesn’t feel that way to you right now, it’s very difficult to put away because you have become addicted to the dopamine and adrenaline and chemical cocktail of the affair.
Ask me how I know…
Been there, and going through the withdrawal of that was absolutely brutal and the best thing for me at the same time. I have also watched this play out with other waywards in this forum for the last almost ten years. Read about romantic infidelity—what you are going through is not special, it’s a predictable psychological reaction to being in an affair.
There is no chance of saving your marriage if you feel you can prioritize keeping the friendship while sacrificing your traumatized wife’s needs and feelings. She has to be number one, and only.