the crap that is trotted out on MN about affairs not being the OWs fault as they have not made any vows to you.
I think the point usually is that the poster is seething with rage at the OW instead of her DP. The comment about OW not having made any vows is not to say she's faultless, but to say that the DP is just as much to blame, plus is the one that the poster should be the angriest with, as he promised her something better. I know ex's OW shouldn't have had an affair with him, but I don't know her from Adam, so can't personally muster up any dislike, even, for someone I've never met.
I got to read some of OW's thoughts in their emails I read, and I have to say that she too sounded naive and a bit thick, to be honest. For instance, he said that when he and I got married we didn't love each other: we'd just "settled" for each other. She then criticised me for marrying someone I didn't love: "why would anyone do that?" So she had no actual evidence of my feelings, but my ex had just told her himself that he had settled - but she didn't think to criticise him for it, or ask him why he had done it.
I'm not sure about the cake-eating theory in our case, though. We were still sleeping together, but I realised later that it was always me instigating it. Ex went along with it, but evidently found it a bit distasteful himself to be sleeping with two women at once. He avoided it as much as possible - waiting until I was asleep to go to bed - and eventually gave me the "not sure how I feel about you" speech, which killed it off.
But all this fuelled my suspicions. If you've been sleeping with your wife and suddenly stop, and refuse her requests, then obviously that's going to make her suspect something. And when you've just started out on your affair, you're not planning ahead to splitting up with your wife and turning your entire life upside down. You're just lusting after a new body. So you keep up appearances with your wife.
Seems pretty clear to me that even a knowing OW would find it disgusting to know that his penis had been somewhere else in between, and would be afraid to catch something. Do men ever admit to still sleeping with their partners? Surely not.