Karma doesn't work in a liniar tit for tat way.
We all know there are many awful people who get away with one horror after another with no shame and no consequences.
And people are stupid. They do stupid things. They do things they regret. They do things they wouldn't do later in life.
Most of them are not getting karma for it. Karma is a spiritual concept that like many spiritual or religious concepts, asks us to accept pain in the here and now for a reward later on, or as a means to control.
I bet there are more relationships that start as emotional affairs than people realise. Especially when the person breaks up and then suddenly has a loyal partner arrive "out of the blue" within a year.
I know many people who have fallen in love whilst in relationships who have then left before physically cheating. But they have checked out of their relationship a year or so before the actual breakup and are having close companionship and conversations with their next partner regardless of whether the new relationships has been consummated or not.
I also wonder how many affairs start now with the internet between old school friends or exes. Three of my friends over the years have paired up with people in this way. Chatting a lot and then becoming emotional crutches to each other and then eventually leaving the partner for. And they've stayed with these people.
And of course the other thing is people who have lifelong affairs but for financial reasons are staying with the person they are cheating on. The internet has changed everything and secret relationships can feel real even if people live miles away from each other, what with sexting and the ability to have real time conversations anywhere you like rather than having to write a letter, use the house telephone, plan weekends away etc. I know someone who has been having a text affair for a decade with their ex from school.