I have no answers - it's the difference in the two sexes and the power of the loyalty I think.
Also nature (I am not making excuses) has provided males with a different impetus than women have - Women being the child carrier makes their investment much
more long term in their makeup and may handle their problem in a different way.
For men it seems a personal slam against their manhood...as if they can't keep their woman satisfied.
Nothing is fair and lucky is the couple who finds fidelity more attractive than wandering.