JaneS, I completely agree with you about feeling so strongly and yet not doing it.
My experience was much like McD's except that the whole thing culminated in DH having a complete breakdown and being hospitalised. It took us several years to rebuild our lives, including his career and our financial security. As our boss she had a lot of power over both of us and she used that power in a very destructive fashion. She tried to have me sacked. She stalked both of us by text, via email and in person. She lied and harassed and manipulated. It was a complete and utter nightmare and very different to the stereotypical image of an affair.
There was enormous pressure on me to blame him and just dump him from many women around me. There was an assumption that he must just be an weak, unfaithful prick. There were plenty of people who initially felt that my fear of and anger towards her was misplaced. There's a widespread, and growing, belief that an affair is only about the couple and a sign that there was something wrong with the relationship and that the OW/OM is irrelevant. Of course that will be true in some cases, but it's too simplistic to apply in every case.
OW haunted us for a long time, even as she was in another city and in the process of becoming entangled in another family - and it does seem to be very much about the family for her. Through her mother I later learned that she had been diagnosed with NPD.
Sometimes relationships break down because they're flawed, or under pressure and not strong enough to handle it. Sometimes people stray because they are with the wrong person and choose to dabble rather than face that, sometimes it's because the straying partner likes the excitement, sometimes affairs happen because two people meet when they're already committed and fall deeply in love.
Having been forced to deal with the complexity of an affair it's confronting and frustrating to read post after post stating that it's all about the one who strays and that the OW/M bears no responsibility. In some cases that will be true, but not in all. It's as shallow and easy to believe that every man who cheats is a faithless dickwad led by his prick, and no more accurate or enlightened than to label every OW a skanky slapper.