To relieve the guilt and anxiety they are experiencing....there are different ways to relieve that: denial, rationalization( assign logical reasons), projection ( to attribute excessively to the environment or others)... The list goes on...,lol that's human.... lol
If they don't justify it, the only reason that they can come up with is that they are a horrible person! A ton of people can't handle that. We're human, we mess up big time, and we have thoughts to do the things that we shouldn't. So be justifying cheating, they never have to face the cold, hard truth. Over and over again.
If they can justify to others it makes it easyer for them to fool themself that they did the right thing...or that there cheating was justifyed in some way.
I used to have a friend that cheated on his other half all the time.
While getting drunk one day i asked him "why".....he launched into a 2 hour talk.
Full of converlutions, contortions, ba
And asked one simple question "have you convinced your self..that what you do is right?"
He had to admit.....even after a 2 hour rant about how it wasn`t his fault and that he was just a man...with needs...
That he was still a scumbag for cheating on his girlfriend.
The same reason my ex used to accuse me of cheating...it is a justification that makes them feel better....they know it is wrong but they feel the need to tell someone be it a stranger or friend.
in a attempt to make it seem like they are not to blame to shift blame to something else so they are not at fault like I was cheated on so it was only fair and then it is not a thing that is thier fault so they can feel less guilty and then when they do it again it will hurt them less to betray the ones they supossedely love
because they feel guilty