“I’ve never once heard a plausible excuse for adultery.”
I have... I heard a good excuse when reading about one of those poor teenage fundamentalist mormon girls who suffered an arranged marriage to a nasty-already-married man who already had children with his first wife.
She quickly learned her role was to babysit and clean during the day and then “service” the pervert at night.
She decided he would not tolerate adultery - so she had an affair with a boy her own age just so she would get kicked out of the house.
Other than that - I would think anyone contemplating adultery really ought to decide whether they are “in” or “out” of the marriage.
If they are “in” - they need to get to counseling.
If they are “out” - they need to make a break before dishonering their spouse.
FWIW, I've known a Hindi couple nearly all of my life, and they've been married well over thirty years now, and they're a delight to be around...the kind of couple that you can just tell really bring joy to each other. That's probably a rarity for arranged marriages.