The devil is in the details (and in that specific case, in romantic stories too ;-).
Reality is rarely black or white, mostly nuances of gray.
Most of the time this is used to demonstrate evidence of cheating (prior to the separation) *in front of the judge* just to lower the other party credibility and gain more money. This is a misleading example IMHO because it seems to be related to love affairs, while it is a very business-like money issue.
BTW, legally speaking, I think cheating one's partner not only is not reprehensible, but it's a right.
Morally speaking, that's of course very questionable.
(And technically speaking, I imagine that's an organizational nightmare...)