'Everyone tells you "he will live to regret it/realise what he has lost etc". But do they every really do that or do they just change the reality forever as in 9 and 10 above?'
I would think that most of them regret it bitterly... but would die rather than admit that to the partner they betrayed!
It's rare that a relationship built on deceit and dishonesty can pan out positively - both know what the other is capable of and trust is compromised from the start. Plus, the baggage...
Most 'OW/OM' relationships fail fairly quickly it seems.
Even if the new relationship survives, or when the betrayer moves on to another relationship, their view of themselves has changed, deep down.
Nothing can ever have that innocent hopefulness ever again.
I think only the strangest, most sociopathic person can truly never have a regret about becoming 'the kind of person who has an affair'.
Even if they spend most of the time justifying and arguing themselves out of believing themselves to be that person.
But, to the one they left... oh no! My life is wonderful. It was your fault. Our marriage was always a sham. Etc. etc.
Lving well, moving on, refusing to engage in any way with the betrayer's commentary on the situation...just showing in every action that they are now better off without them... that's truly the way to get revenge.