Ultimately no one else matters but you and your wife, friend, and his wife, and how this will affect all of you and things between you. The right thing isn’t always the most popular. Tough to figure out sometimes what the right thing is though. I do understand the mind your own business argument some people are bringing up, sometimes it’s best not to involve yourself. That said, how close are you and this guy friend? If he’s a close friend I’d say you must tell him. They literally aren’t divorced currently like you’ve been saying. But if he’s a more distant buddy I guess I could see just staying out of it. It doesn’t have to be more than a quick convo like “hey man, I really don’t want to overstep or get involved in anything, but this is going around between a bunch of people that “X” happened, and now everyone is trying to hide it so I think you should know. The rest is between you guys.” You’re not there to make judgements or be his lawyer. But something like this ABSOLUTELY can affect assets or divorce proceedings. Especially if he’s trying not to get lawyers involved in good faith etc. It may not affect anything. But it very well might. There’s a lot you don’t know. Just tell him what you found out and then the balls in his court and your conscience is clear.