Interesting subject.
My WW's first A was while I was away for 3 months, out of state, starting a new job where we had made plans to move. She and my 2 children remained behind while our house was being sold. We had moved where we were living 6 years prior, with no other family within 2 hours, had few if any common friends, heck we didn't really even know our neighbors. That A was carried out in our home, relatively out in the open as far as I know. Our children were 3 and 5 at the time so I'm sure it was easy to hide it from them. I was 1000 miles away, easy to hide from me. I will say her attitude grew increasingly distant during that 3 months, toward the end she even said she didn't want to move, she wanted to and keep the children with her. I know I suspected it, but I don't think I would allow myself to believe it. I didn't find out until just after I basically forced her to move and she was forced to tell me she was pregnant, obviously not mine.
Her second A, was the next year, we had moved back where we moved from, I know bad idea, and ended up separated. Again, I wasn't close at hand so it was relatively easy for her to get away with it. Same OM as A #1.
Her third A, an EA, started 15 years later, texting and some phone calls, phone kept on silent, fake name in contacts, me apparently not paying attention to any of it and I never looked at the phone records. It was likely my lack of attention that made that possible.
Her forth A, a PA with the same OM as A #'s 1&2 began 22 years after A #2. She still kept her phone silent, had a fake name for him as well, only talked on the phone from the car. Lied that she was going out with work girls or the like when they met at hotels or to make out in his van. She paid all he bills with our credit cards, she paid the bills, I didn't look. I was completely oblivious. I really didn't pay much attention to her, our relationship was pretty much non-existent so again, my lack of paying attention was a huge factor in her being able to get away with it.
The day I discovered the EA (A#3) I also discovered the PA she was having at the same time (A#4)
I choose to take a chance on a serial cheater from the beginning, I was too dumb and naïve to understand the risk. That was a costly mistake. I chose to give her a chance after the first A, that was a costly mistake. I have given her yet another chance but she is on the brink of losing it.
So...how did she get away with it? Some ways were just convenient circumstances, some by her secrecy, but mostly my own fault, chances I should have not taken from the beginning, second chances that should not have been given, attention not paid, even when I knew better. I'm not sure who it's harder to forgive, her or myself?
ME: 60 Madhatter, 1 PA, 6 months(making out, no sexual contact), 2006. 1 sexual act with a stranger in a car - w/hands, 2010.
WW: 57 Madhatter, 25 year (1988-2013) PA, 3 separate affairs, same OM). 8 year, 2005-2013, EA with 1st boyfriend/lover