I didn't want to get personal in this thread, but your comment invoked a response from me. I also might be able to better help the OP understand why some people think differently on this subject so here goes nothing.

I disagree with the notion that "real men" look out for everyone and here's why:

Unless you're a police officer or are in the military or you live in a small village or tribal community where needing to protect others is important to your own survival, it isn't your job nor your responsibility to protect everybody.

To me, a "real man" is somebody who possesses both the strength and courage to defend whatever or whoever he holds dear no matter what. Most of us live in medium to large sized cities where we don't need to rely on those around us for survival, therefore, there is nothing wrong with not caring about every person in ones community.

Humans, like virtually every other living organism, are selfish in nature and are genetically programmed to care only about surviving and procreating. While we, as humans possess superior intelligence and can thus, navigate away from our primitive biological directive to some extent, not doing so doesn't make anybody less of a man or woman.

While I don't defend or justify cheaters myself, beings that the only people that I owe any loyalty to and the only people that I would consider risking my life to protect are my family and friends, if one of my friends or family members cheated on their spouse, unless I was also friends with the spouse or I had a really good reason to, I would keep and defend their secret (regardless if said friend was male or female) out of loyalty and respect for the friendship or relationship. I have a hard enough time as it is opening up to people and making friends who I can trust, so I make it a priority to keep what few friendships and relationships that I have at any cost. I consider my friends and family my "tribe" or "community" if you will and I seek to defend it at any cost.

I don't needlessly hurt people by any means and I even would help a stranger if they needed it, but I stay to myself and I ultimately put members of my "tribe" first before any stranger.

With that being said, it take a rare and an exceptional and highly special individual to be able to care about any person as much as their own friends and family. Just because somebody isn't like you described doesn't make them any less of a man or woman the same way that not being a professional MMA fighter or boxer doesn't mean that I can't hold my own in a fight or not being the CEO of a fortune 500 tech company doesn't mean that I don't know my way around a computer.