You are right. No one is disputing that it is an exit affair. These are cowardly, lacking in integrity. That is all that is being pointed out.My "advice" is that there really is no advice to give. While the OP did a terrible thing by cheating, I actually think she is showing more courage than I ever did by leaving the marriage and being willing to tell her husband the truth about the affair. When I was a wayward I spent a lot of time listening to negative reinforcement about how awful I was, much of that was on forums like this. I took advice from other wayward spouses that told me the best thing to do was reconcile. Nobody ever bothered to ask me if I actually loved my wife. Years later a therapist did.
After years of false reconciliations initialized primarily because of guilt and because I thought I could "fix" myself, ultimatly all I did was cause more pain, and delay everyone including my own children from moving on. So I think the OP has it right. Tell her husband the truth and file for divorce. As for the AP, it might work out, or it might not. But I could say the same for any man that she decided to become involved with. If it doesn't work out, it certainly doesn't sound like the betrayed husband is a plan B. I don't think she wants him anymore. So basically I agree with the guy that says this is nothing more than your standard garden variety exit affair.
And, the odds of success may be impacted not only by the integrity of the two participants, but by the fallout. She may have familial disapproval, ex spouse resentment, and some stigma to deal with, as well.
In my XW's case, the kids hated the OM. Her family banned him from ever setting foot in their homes.
She had an honorable option, divorce. It is straightforward and simple. Mainly accounting. Yet, she chose this path. That speaks volumes.