I could be totally off base here, but I just wanted to throw something out there. Having done something so out of the ordinary for you, (as attested by yourself, your husband, and g/f), is it possible you self-sabotaged?
Feeling that your triad was slowly coming to an end, is it possible you were trying to speed up the process so that the unknown could become open and known to all three of you ? That the pain could somehow be lessened by not having to wait for what you thought was going to be the inevitable outcome?
Having read your posts, you are obviously as honest as you know how to be with your feelings, thoughts, and emotions. To do something that goes against all that you believe and having to admit to it, could just be a way of taking it on yourself, and leaving your partners to take a lesser role in what you thought what was the possible end of your relationship. You did what they couldn't, but didn't know the best way to do it, so did it the only way you knew could break trust.
It allowed what needed to be discussed, disscussed. Forgive me if I'm totally on the wrong page. I just thought it might be something to think about.