I hate to agree with majority over minority here, but I really do think that cheating is NOT acceptable be you a male or a female. I say this not only as a person but as man. You have to becareful not to overgeneralize cheating (Painting it as nothing more than just some casual fling with no cause for distress). Cheating is mostly a heavy investment in the OTHER person of time, affection, resources, while the SO is left as a nobody.
...And EVEN IF it wan't a heavy investment of the above from the guilty party, cheating in itself is the breaking point of Committment and Trust, which is the fabric that binds the relationship together. You cheat you break the trust, this trust is irreperaible and this concept is undebatable. Your partner is the person you trust with everything you hold dear in your life, all this is shattered when you can not trust that person anymore. Trust by the way (Unlike arguments about marriage) is not a religious construct, but a moral construct. As an example from our modern culture, you default on your loan or claim bancrupcy, no bank that has a history of your conduct will ever give you another loan (Because You broke the trust and your credit history is gone). The same holds true to every relationship, you break the trust and there is no point in continuing on because all you have left is endless uncertainty, doubt and worry...
I thought i'd throw in my 2 Cents
Don't cry, don't regret and don't blame
Weak find the whip, willing find freedom
Towards the sun, carry your name
In warm hands you are given
Ask the wind for the way
Uncertainty's gone, your path will unravel
Accept all as it is and do not blame
God or the Devil
~Born to Live - Mavrik~