well men get triggered by what they see BUT they can bond to one person and stay faithful even in their mind. Love is not only hormones and semiochemical substances. It is also a part of the mind. you can learn and control..Especially men as they are more thinkers as woman. Thats the main opposite they have in them against their natural reproductive instincts.
Men do also get a release of oxitocin when they love, as in chemical is not much different from the Womans, just that they show it differently.
Thing here is that he seems more attracted to other woman, maybe due to a lack from his current marriage (idk or hes just an dumb dumb), and hurts her feelings. It does not even seem to me as if he wants to work things out and stop cheating in his mind. Hr could do something against it, but he wont
now what do you mean with
"The only mystery with people is how we could have gotten so far being this stupid."