Dunno if this counts as deep OR dark ~ a few years ago my then wife and I were visiting with friends. Somehow I wound up sitting between both girls, with HER husband out to the off-licence (liquor store, for my transatlantic frineds!) watching a video and chatting. (BTW, this girl and I had enjoyed a very flirty relationship for years)
Anyway, after a while I had one hand fondling my wifes right breast, the other fondling my friends left breast ~ and neither of them ever knew!! A fun time for all, cos they both thought I was only doing it with them, and they BOTH got really horny!

Bit boring, on reflection (sorry ~ had to be there I guess), but still - it's a SECRET!

__________________
The selfish, they're all standing in line
Faithing and hoping to buy themselves time
Me, I figure as each breath goes by
I only own my mind