Well, these aren't secrets anymore by now, but they were for quite some time during our relationship:
Husband: I used to encounter an older couple to have sex with them while I was single and younger. Mostly fucking that wife while her spouse watched and gave directions. But as the encounters turned more frequent and intimate, then I went further to fuck them both - the man enjoyed dick from his wife's pussy into his own mouth whenever he got very horny. Of course wasn't my initial plan to expose this secret to my wife, but as our sexual relationship deepened to a non-vanilla one I exposed it for much of her surprise.
Wife: When we got married I couldn't design or guess the real amount of cock that my wife already had pleased and tasted. Within time after I could dig much more inside her sexual preferences and roleplay, so she finally revealed her thrills for having herself photographed naked and sending photos to other men since her sexual life initiated. More than just that, I discovered she kept sending naked photos to a man overseas (Turkey) that she randomly meet by chance online and kinda of became a habit of sending nude or masturbating photos to that guy, expecting to receive compliments and texts in return. A habit that she maintained in secrecy from me as a husband already, but now she is able to do it shamelessly so.