Woog, this sucks so bad that your S was exposed to this. I can probably guess that he will talk to his brother and sister about it. I also have a pretty good idea where your emotions are right now - anger. Totally justified anger. Give yourself a bit of cooling off time before going to the L, however, I suspect that even with time, your W has crossed the moral line in your mind and you probably will decide to file a D.
You do now seem to have pretty good evidence of adultery. Idaho allows one to file with various grounds for divorce reasons (fault) as opposed to just the irreconsilable differences (no fault) that Oregon has. Alimony is decided upon various factors and the fault plays a part. Also, I believe that Idaho has only a 20 day waiting period. Your W may discover that inappropriate actions have a consequence.
The decision and control is now in your hands - be true to what you want. Dont make any rash decisions that you may later regret.
