For example (my situation... and yes I'm still faithful), I've had a very difficult marriage... because my wife has failed many aspects of the marriage contract. Sure, she's been faithful... but she has made my life hell... I'd rather she cheated than be as nasty as she is at times.
And yes, I was close to divorcing her... when she got cancer. Out of loyalty, honor and compassion I'm still married to someone I'd rather not be married to... Oh and I should mention... I haven't had conjugal relations in a long time (and I'm fairly young) So if I cheat in the future out of sheer human desperation ... does that make me a monster? According to you it does. I guess I have no right to have any happiness in my life.
This puts a different slant on what you had written earlier about serial monogamy. Some marriages don't work out too well ---but most people don't enjoy divorce and most would prefer a long term but happy marriage. Even in bad circumstances, loyalty, honor, and compassion are traits humans tend to have including men which infers long term monogamy is natural.