Due to the nature of the users on this forum, the answer is always of course, hell no to cheating, but as iv said before on this topic its never ever black and white and clear cut scenrios never happen, its way to complex and as ever, society has morals influenced by religious background, think about it, if 'cheating' was the norm and you were bought up to know this, you would never see it as a bad thing, its just society has said its bad. Why am I saying this dear reader?, well naturally humans are NOT programmed to be monogamous, naturally both male and females will sleep around, 99% of the natural world this happens (aside from a handful of speicies where some genetic trickery has made them to generally mate for life, therefore its natural to them to be monogamous)
Of course a lot of people have long and happy marrages, and thats great, a conciously focused decesion like this can be very rewarding, but notice how everyone says most of the time it takes effort or nearly all people have a few relationships ? especially recently ? its because the natural human desire for sex with attractive people overrides, our instinct is who we are as a species. I suppose peoples general viewpoint is it happened less many years ago, yeah probably, because religion had a more powerful place in peoples lives, but I bet it happened a lot more than people ever admitted.
So I view it from the viewpoint, everyone is human, if my mrs cheated on me yeah it wouldnt be ideal but I fully understand how it can happen, and would look at the circumstances and such, you just have to think about humans, as a human, its kinda weird how influential society can be, even though most members of society probably think more or less the same (which isnt what society says as a whole)