That's the main difference between men and women. Women live and die for gossip and any juicy tidbits about people. Guys don't give a damn about that crap. Women consider it a crime worse than murder if you know something about someone and you don't share the dirt and tell the person you know what's going on.
This is a massive generalization. We aren't talking about just someone on the street. We are talking about her friend. That isn't "sharing dirt". As someone else pointed out, when you help maintain a secret, you are in fact being more loyal to the other party. Again, if they are my friend, I would expect them to be more loyal to me than my husband who is LYING to me.
And, if it really so ok, why would it take guys some time to eventually be ok with it? I wonder if they actually decide to not make a big deal about it, but mentally place this friend more on the outside circle without discussing it.
You cannot generalize all information as gossip.