We can agree to disagree. When both parties do what needs to be done, it works and it works particularly because both partners are usually acutely aware of what is required to have a good marriage.
Even in my sitch, H left 6 years ago and yes he had an affair and came back. We were in therapy and for a long time we had so much gratitude for each other and the marriage. Then we got lazy about it (him first of course ;)) But, I know from experience what is possible when both partners make it the priority.
The trust was only tough if my needs weren't being met or if we were not getting along which was pretty similar to any R. And, quite frankly, having lived through it, a sexual dalliance was not my worst fear.
Again, most long term marriages deal with infidelities, separations or betrayals of some kind. The decision to reconcile and the work it requires often strengthen the M. It is all relative to the value both partners are willing to place on maintaining a better M.
