Karma is a patient, harsh, and vindictive bitch. She'll get hers.
Bull shite. People who believe in karma are losers. Your life is what you make of it and waiting on some cosmic revenge is fricking stupid. If your SO wronged you in some way by cheating, then fight dirty. Hire the nastiest lawyer you can find, protest every single thing in court, generally make their life a living hell, and only contact her through your lawyer. Only when the dirvorce is complete should you stop giving a shite.
The reason I say this is because the overwhelming majority of people who frick up like this never receive any bad karma from it and then they go on to do it again and again. This is also why there are so many terrible people who hold office and lead companies.
If you're waiting on karma to solve shite then you're almost certainly going to be waiting a long time.