This in no way gets at the heart of the matter-why she cheated? What was the underlying reason for infidelity? The blame for her behavior in the affair is 100% hers, but the blame for the underlying problem in the marriage is 50/50 hers and his. I don't believe you can add the sting of a confessed affair to the equation, before you work on the underlying problem. This should be a 4 step process:
1 End the affair and cut all ties - you cannot work on the underlying issues while still in the fog (your head/emotions are all scrambled up), not to mention it is flat out wrong
2 Get to work on addressing the underlying issues in the relationship, if the partners cannot, will not, or don't want to, then it's time to start the D process
Non sequitur. You cannot resolve issues in a past -> present sequence, you must work your way backward. You do not start with the first problem in the relationship, you start with the most recent critical one.
Starting with the elephant in the room -- the affair.
Plus, you have to give back what you've taken away -- the ability to make a fully informed decision about the rest of their life. Affairs have an element of informational fraud about them -- you don't start fixing fraud by talking about what led up to it. You start fixing fraud by giving back what you took.
And you missed the whole "maybe we both need to get STD tests thing."
3 Recommit to making the positive changes in your relationship, to begin "phase II" of your marriage, and enjoy the new you and her dynamic
Which can't begin with a lie. Because it all will be a lie.
4 Once you can understand the underlying reasons for problems you used to have in the M (but no longer have and you can see the difference with time), then you can show the clear connection to why 1 party would want to have an affair, and it will make sense. Details about the A can then be shared, and the sting will be greatly reduced because the BS understands the why, but also has benefited from a positive turn to the M and wants to continue
BS. The sting will be 1000x worse, because you will have just drug them through the mud, and cleaned off, and you just threw them back in it.
You seem to get a sense that the person having the affair gets to make all the decisions for both parties. Why is that? Especially given the power asymmetry involved?