Focusing first on what Mosman decided to do in contacting the OW for a moment, this can be a risky but ultimately healing experience for the faithful spouse and I'm very glad that it proved to be so in your case Mosman. Often, the OW or OM in these situations can take on mythical properties in the minds of people who've been hurt and it can be a helpful exercise to communicate in a calm and factual manner because apart from the opportunity it gives to correct any misapprehensions on either side, it also tends to divest the other person of the power s/he is still wielding in one's life.
I would add that very few OW/OM who are now distanced from the infidelitous relationship concerned, espouse this view that they had no responsibility for the hurt caused to themselves or others. However, it is a common and understandable delusion held by people who are at heart selfish and are poor at taking personal responsibility generally, those who have remained in the affair relationship and in those who are on the precipice of an affair or are currently involved in one.
Concentrating on the more general points made, it is an astonishing fallacy that affairs only happen when there is relationship discord. In fact, even if there is relationship discord (as there will always be at some point in a marriage) this will never, ever be the only reason an affair happens.
I really liked an an analogy a poster once shared on a Mumsnet thread, which had come directly from her personal therapist. The therapist said that when a vehicle is involved in a serious collision, an investigation takes place to reconstruct what happened. In the vast majority of collisions, driver error is the primary cause. However, even when this has been proved to be indisputably the case, it sometimes emerges that one of the vehicles had an unrelated fault, such as a balding tyre. In some collisions, that balding tyre might have been a contributory factor, in others not at all. But it would be as iniquitous to say that the presence of a faulty tyre was the sole cause of the collision as it would be to say that an unsatisfactory relationship is the sole cause of an affair. And in some collisions, the tyre issue wouldn't have been a factor at all, just as a normal, unexceptional relationship is very often not the determining factor in whether an affair will occur.
The ultimate determining factor resides with the individual who chooses to have an affair or to become involved in a triangular relationship.
The starting point in all affairs is what life coping mechanisms an individual possesses. These vary enormously from person to person but simplistically, whereas an emotionally healthy person will boost their life esteem through healthy, slow-releasing boosts such as those derived from partners, friends, family, their careers or their talents - an addictive or egotistical personality will reach for 'quick fixes' such as affairs, gambling, substance misuse or a sex industry experience. Likewise people who are depressed, bereaved or meeting a life crisis will often choose an affair as a quick 'high'. The quality of those very differently motivated individuals' sanctioned relationship can have very little bearing on their choice of coping mechanism. The common denominator however is that those individuals (sometimes only temporarily) have poorly functioning coping mechanisms.