Honestly, I don't recall how I learned the 'man code' (the understanding that some information that guys share between one another is only ever spoken of between one another - period).  I don't think I learned it from my father (he didn't talk much about anything - different issue).  Mostly, I think that I intuited that some information, particularly about one another's behavior, was best kept to secret.  I imagine women have the same sort of honor code.  But, I don't know what it's called ('sister code?').

Anytime you share with anyone something you want to remain private, you take the risk they will tell someone else. It's always been that way. If you really have to discuss something that you want to remain private, pay a therapist.

...it's not what you describe.  

from a married man.  If you wouldn't share it with his wife, don't tell him.  This is especially true regarding couples who are friends with another couple, less often when the wives are not friends.  It starts by your friends wife saying to your friend, "Betty thinks John might be cheating on her."  Now your friend is in a position that if his wife later finds out he knew and didn't tell her, she will think she can't trust her own husband either.  So when confronted by his wife, your friend will spill his guts about what he knows.  Its better not to tell anyone. I know tempting when you're fucking some of hot women in this biz to brag a little, but no good can come of it by telling your friends if you're married. Just my take after seeing it blow up with some guys I know because they told their "best friend."

Bro codes
It's that I don't trust them or sometimes it goes the other way around:  
rather not get involved

And we're an older group so when one dies, it's one less worry....lol
But if what we know of each other ever got out, well let's say it would get a little messy. But seriously now, our wifes or SO know what goes on when us guys are on the loose, they tolerate because we always go home to momma.  
But...."Loose lips sink ships"

I live by the code and will die by the code.

I'm cynical about the 'if his wife later find out he knew' premise, because that would require that I told someone that I told him.  Even if that were to happen, I would sort of understand the 'caught in the act' confession.  But, I'm sad to report that the most serious breach of trust was just a case of my friend making conversation with his wife. (still griping)

Yes.  'Bro Code'!  Thanks.  I couldn't think of the current vernacular.  

Good advice Cat.  I certainly know that now.

single guys to say, but its more complicated when you are married and have friends that know who your wife is.  

I would never snitch.  Some things are better left unsaid.  My wife knows full well I fuck young sluts.  We don't talk about it at all now.  We have a life together and will grow old together.  Me getting my meat slurped by some slut has nothing to do with that.  My close friend would never say anything.  I would not say anything.  My wife doesn't want me to say anything.  All this honesty stuff is bullshit.  

Not talking about it by mutual agreement isn’t the same as not blabbing about something a friend said in confidence.

Guy code existed in my fraternity. It was drilled into us as freshman.  

is probably dead today.   The pussies in college these days won't be able to take the  pressure of keeping a confidence from a frat brother and will need to spend some  decompression time in a "safe space."  Lol

Im planning to be honest with my wife too. No whoring.
Being honest about anything that involves her or me.

Agreed.  Your points plus drugs.  My chapter has been booted off campus twice for drug possession.  

"Three people can keep a secret if two of them are dead."