An affair is like a chronic illness.
There may be times of remission, but it will, in some form, return. Go into recovery with no illusions that it will be otherwise.
This is not true, and you shouldn't be trying to dishearten posters - especially those currently telling with affairs - by telling them this.
This happened to you. You have no overview of other people's situations that gives you the right to say that this will inevitably happen to everyone else.
Dr Harley has supervised recovery for thousands of couples, and he knows what makes contact recur, and he knows what makes it impossible. Exposure of the affair on both sides, a No Contact letter handwritten by the WS, and a refusal by the WS to entertain any further contact from the OP are acts that send the clearest messages to the OP that the affair is OVER and they are not to intrude in this marriage again.
Where necessary, a change of job and a new start far away from the location of the affair reinforce that message to the OP.
From what I remember of your story, you didn't find out about your H's secret second life until long after the affair(s). Did he end that affair cleanly? Was it exposed to her circles? Did he send an NC letter? Did he repel any advances from her after she tried to keep the affair going at the time?
If he didn't do those things, and if they parted perhaps with lingering affection, that would explain why she wonders about him today, and thinks nothing of hurting you by contacting him again. If, however, YOU exposed the affair to her partner and parents, and let her know that your husband was not her boyfriend, and she had better dare not interfere in your marriage again, and if you issued an ultimatum to your husband to ditch her, change his job and move, or else, and he did those things and refused to give that woman hope - it is unlikely that she would be reaching out again today.
How did this affair end? I think you need to look at the loose ends that allowed this contact to happen, before you tell everyone else on this board struggling with an affair, or tentatively entering recovery desperately using Dr Harley's guidance, that an affair will in some form return, and they should go into recovery with that certain knowledge.
Shame on you.