I don’t even believe that statistic anymore; maybe thirty years ago, but no more. In fact, as women are increasingly divorced or having babies without marriage, the rules of those circumstances skew the stats against them. For example, if you marry a woman that fits either of those categories, you must understand that there is absolutely no problem (in her mind) with continuing to maintain sexual relations with the former spouse/baby daddy.
“Unfaithful” is a term I associate more with marriage than simply dating, and as marriage goes the way of the dodo there is less likelihood that a man could ever be “unfaithful”...
Bringing in the statistics on cohabitation into a discussion of what gets awarded at divorce introduces irrelevancies. See my post just above.