Had kinky sex with my wife’s friend (before we met) and I can’t find a way to tell her.

To keep this short and to the point my wife goes to yoga and often goes out with people from her class for drinks afterward, occasionally she will invite me to join her. A few weeks ago she did just that and introduced me to a new friend she made, I’ll call her Alex. I had met Alex years ago, in a whole other state, when I was on Fetlife. Alex’s kink was CNC. We got together because I’m vas safe and very good at roleplaying do I thought we would be a good match and she agreed. We met a few times, she was married then but her husband allowed her to play with others to get what she needed and he wasnt comfortable doing. To the point if it was just a casual vanilla situation I would have had no problem telling her we had been involved in the past. This was anything but that. My wife is a SA survivor and it was very traumatic for her. I’m beyond 100% certain Alex remembers me but didn’t say anything. I feel guilty as hell about this and know she would be devastated if she found out.