I know that the main reason that my wife left was so she could sleep with the new guy with a clean conscience. Who knows if she was sleeping with him before, I just don't know. But in her head, once she "left" it was fine.
I got two bits into your post and thought 'OMG - that's what they do' . . .
In my recent, ':)ear John' eulogy, my pay off for putting up with two and a half years of crap, she ended up saying 'It's not because I want to want to be with anyone else'. The atmosphere juddered and I checked what she said.
Next time, ten days later, we talk she says 'I thought we already talked about this . . .' I had to apologise for not realising she had already moved on so fast- idiot me - it's what they do. The ground has already been laid (ahem!) - a lie ahead of time to salve conscience. Too bad.
For the record, she did exactly the same with her previous husband - precisely so she could preserve honour and sleep with the new guy with a clean conscience. It was hubby's fault he did not fight hard enough . . . never the BP's fault. And they say history never repeats itself. Go figure . . . sad but true.