To me that says cheating all the way. S and I discussed exactly what was acceptable and not before I even went out with my bf. I talked to my bf and told him exactly what S and I discussed and exactly how far or how far its not gonna go. The relationship S, bf and I have as 3 people started around 18 years ago. We all know each other very well. As far as me dating(or whatever you call it) my bf, is actually very recent. And in the end it doesnt matter if I knew him 18 years or 18 days. If S is not comfy with something I dont do it. To go against what he specifically asked not to happen, well that would be cheating. And if he decided he wasnt comfy at all, well then the relationship is over with bf. I love my bf dont get me wrong. But S is my primary. He is my husband. And I respect him enough to not do anything that would make him feel uncomfy.
Im sorry for what your going through. Thats a rough situation that I know personally I would be angry in and trust issues would be a thing I might never get over. Good luck in what you decide to do. HUGS!
She is C He is S