Irregardless of whether or not you were alone or not, you (at least physically) cheated on your W. And before you go on about how we don't understand the lifestyle, etc., we've had numerous people in poly or swinger type relationships so we do get it.
The thing is that even though you say you had "boundaries" put in place, because you are exposing yourself to other people, those boundaries don't exist. You can't "order" a person not to have feelings towards someone else, especially if they are receiving pleasure on an emotional level from that person.
Can you detail the rest of your marital history? How long you have been swingers, etc. And if your kids know, if your W is now exclusive to this OM, etc.
M-43 W-40 2D - 9 and 5
Emotion, yet peace. Ignorance, yet knowledge. Passion, yet serenity. Chaos, yet harmony. Death, yet a new life.