[user104658]

Bit of a dual answer here. If something is said in confidence then I will keep it that way - with the caveat of understanding that if you tell me something, you are telling both me and my wife that thing. We talk about literally everything. Essentially it's not just that I might tell her, I 100% definitely will tell her, and vice versa. However for both of us, it will go no further than that.

I think that should generally be assumed of most long term/married couples, though.