My dad's entire years long affair was conducted almost exclusively on business trips. They lived 1,000 miles from each other. They met on a business trip. (They are married today.)
Anyone who works full time can see how an affair can happen. We spend more quality and quantity time with co-workers than we do at home with family. I have never been married, and I am in my 50s so this ship has sailed, but I would never ever be a SAHM. Ever. It makes you underestimate what it is like being away from home working so much and bonding with random people. The working spouse has a totally separate life. The SAHM is running the entire show at home alone. He gets the benefit of being a Family Man with little or no involvement or effort.
Of course being a SAHM allows for ample time and opportunity for mom's affairs as well. It's not just the men. But according to my dad, he just lost respect for my mother, the SAHM, when he was spending so much time with working women who had much more interesting lives, dressed nicer, had more to talk about, took care of their appearance, were financially independent, etc.
When my dad came every night from work, my mother started nagging him for one thing or another from the second he hit the door. Oh, it was such an unbalanced relationship!
I see affairs happening over lunch, on business trips (real and fake), Happy Hour times. It's so utterly common it doesn't even raise eyebrows anymore.