I am now involved. It did not "just happen". I consciously knew what I was doing. I calculated every thought and emotion I was allowing to enter my mind. Every word I said to him brought us closer to a unspoken precarious ledge over which we pretended we wouldn't fall... This is how an affair starts...
I am intending on saving this to my own blog - truer words never spoken. I told my FWSO this was what the deal was, he just kept saying "It just happened" This is not a 2x4 and please know as a BSO I am not sympathetic but I do appreciate the honesty of how you "fell" into this.
Now how do you stop? Just like a car with brakes - you just do. If you see a brick wall in the road ahead, you don't smash head on, you stop & save yourself. Do that first, brakes. I would think then you need to do what you can in restrospect to his BW. I cannot tell you to tell her as a OW, I only know my perspective.
I can feel your conscience and I think you can to otherwise you would not be so...well you wouldn't be here.
Good Luck, I wish you peace in your future.