Me too. But if a good friend tells me something sensitive that is supposed to stay secret I would perhaps not tell my SO (assuming it's none of her business in the first place). In return I would accept she would not tell me everything her friends tell her. We could (and should!) share a lot, but not everything by default where it comes to certain family and friend's peculiar stuff. Also, sometimes even when you love your partner to death and would like to share everything with her, it is good to realize and accept she's not good at keeping a secret So it is not like you wouldn't like to tell her, it is just that you know there's a big chance she would tell someone else she trusts (best friend, sis, who knows). We all knows how gossiping works and rumours gets spread. (by people we trust and told a secret anyway ). So yeah, depending on the info and the people involved, AND the SO of course (as I am only speaking hypothetical atm).. I wouldn't. But it's cool if it can be shared. Seems to be the ideal situation.
I've never dated a super gossipy person. I guess if it were a secret that had nothing to do with anything that would come up or be relevant with my SO, I might just keep it to myself. Like, I could see telling my SO if it would involve me having to lie to them about what's going on with my friend or whoever has the secret, if it affected us as well. I suppose it also depends on whether your friend is close with your SO. It's tricky business, haha.
I don't tell my SO everything. I think it's foolish. If it's something that would concern her then sure but otherwise not her right to know.