I didnt mention "Karma", which I personally dont believe is the same as "What goes around, comes around"
Personally I'd use those interchangeably but I think we are talking about the same thing - if you behave badly, you will get your just desserts in the end. Bad behaviour ultimately will come back to bite you in the ass - that's the theory under discussion.
Whatever you call it - I don't believe it is true. I think sometimes it may happen by chance but it doesn't follow at all and there are far more examples of people behaving badly and getting away with it.
The serial MM who cheats and cheats until the day no one wants him anymore and he ends up alone.
For everyone like this there are dozens who do cheat and cheat and don't end up alone - whether because their wife turns a blind eye and puts up with it until he is too old or infirm to pull any more, or because they cycle through women or because in the later stages of life they have stacks of cash and can attract a younger women.
Kirk Douglas, Tony Curtis, Alan Clarke, Cecil Parkinson are just a few examples off the top of my head but there will be hundreds more and these are only ones we know about because they are in the public eye.
What goes around comes around is a total myth.