I cheated on my spouse with someone who doesn’t share their same kink

so I kinda did something I’m not sure how to explain... we just got back from our last vacation together and everything was fine. then a friend of mine mentioned this other person online, someone into something my partner’s not down for. it started off as an email exchange but ended up being more than that one day. i didn’t tell them or anything cuz honestly it kinda feels like cheating even if we never talked in real life... i know my wife would freak out if she knew and I’m just trying to figure out how bad this is and whether i should come clean...