I would not mention anything to H about what you learned. You say you feel you are being sucked into the drama... so go with your gut feelings and stay out of the drama.
Whatever you say to H about the OW will only look like you are jealous and trying to break up what they have. H will not look positively on this. Remember he is not thinking clearly these days. This relationship with H and OW will end and it sounds like it wont be pretty when it does. To the extent you can stay out of it you should. You will feel better about yourself in the long run. Also try not to talk about the situation with Mr and Mrs S, again to the extent that you can stay out of the mess and try concentrate on "you" and the kids then you will feel that much better about yourself. Feeling good about yourself is the ultimate key to staying strong during these very difficult times.
