Putting aside the obviously grotesque thing that this guy did to her sister, it's always interesting to me how in western culture we arguably have the complete opposite extreme as what we would see in Eastern and Middle-Eastern cultures. Here in the west, our culture is basically infested with cheating and extra-marital affairs and many of us have probably become desensitized to these things so much that it almost seems normal. I mean, we even have dating sites for cheaters like ashleymadison.com.
Then you have these Islamic nations that take cheating and extra-marital affairs very seriously. It's not only shunned culturally, but even the government intervenes and stoning to death or hanging isn't uncommon in countries like Iran.
Both extremes are bad in my opinion, but at least in these Eastern and Middle-Eastern cultures, you at least help to maintain the nuclear family by shunning cheating/affairs. I mean, what typically happens when either the man or the wife cheat? Fighting, divorce, family instability and you basically emotionally screw your kids too.
Let me also add that in countries like Iran, getting a divorce is much more difficult than in the states. You typically need the husband's approval and there is no such thing as "no fault divorce" which makes either the husband or wife able to divorce whenever they want for no reason.
Do you see where I'm going with this? The point I'm trying to make is that making cheating wrong as part of the culture, taking extreme measures when cheating occurs, and making divorce harder to obtain all make it so that the nuclear family doesn't dissipate like it did in America, and breaking down the family has horrible outcomes for children.