Saying someone is boolean "good" or "bad" is of course complex - perhaps beyond utility. But to the extent a moral evaluation is being made of a person (unless your point is no such evaluation can or should ever be made?) I don't see how their conduct in their romantic relationships could be exempted?

Yes, it does. Abusing your spouse is one of the worst forms of abuse, especially during that time, because they can't really get themselves out of that situation. Cheating's a more intense version of any other breaking of commitment. A person who consistently breaks commitment is absolutely an awful person.

There are however many other metrics of what makes someone good and bad in a moral and human sense.

Sure. A child-beater can donate millions to charity. An anti-consumer monopolist can donate billions. A rapist can volunteer at homeless shelters. None of these are good people: their worst aspects are inexcusable.

So please, lay off the "if you ever cheat on your wife you must be a piece of human garbage" nonsense.

Do it multiple times to multiple wives, you're definitely human garbage.

You can't magically compartmentalize away being a terrible person solely because you're only terrible to a single person who has very little power. If a person who tortures someone—just a single person—has good actions outside of the person they have locked up in their basement, they're still a bad person.