I really do believe they start to believe the bs they tell others, its like they think if they say a lie often enough then it must be true.
Two days before my H moved out we had an argument, H said to me "remember about 20 years ago I asked you for a divorce????????????" Um no never ever happened. Let me say this 20 years ago we had no kids and were married about a year and I moved from th UK to the USA with him and I was so miserable, I missed my mum and dad my 5 sisters and 2 brothers all my friends, my home, my country , the food I could go on and on. So needless to say in my frame ofmind at the time if he'd offered me an out I would have been GONE!!!
So yes I firmly believe that they believe their own crap.
M 41 H 43 M 22 S 18 S 14 D 11 Affair discovered 1/12 He filed 2/12 OW#2 7/12 she lives next door. D pending