As I read through the forums on Divorce Busting, I like to grab the nuggets of gold and share.
My advise, commit to personal growth. What you judge in others, you condemn in yourself. Take all the focus off of your spouse and address your own issues. How hard is it to change your own behavior? Now think how hard (almost impossible) to change someone else.
If you have kids, commit to being the best parent ever. Frequent and equal contact with both parents is important. You are responsible for your relationship with your kids. Let your spouse be responsible for their relationship with the kids. Learn new ways of parenting. Lots of great books out there. Most of the relationship skills dealing with spouse will also help in parenting.
Set goals for the future and keep taking steps to get there. Do this in all areas (SPIES - Social, Physical, Intellectual, Emotional, Spiritual.) Get in alignment (Beliefs, Thoughts, Body Language, Tones, Words, Actions) with your core values.
Try new ways of interacting. Read about boundaries and learn how to set and enforce them. Be in the present. Let go of the past and do not fear the future. Learn ways of being more attractive, especially in your behavior. Learn ways of being seductive (indirectly attracting). This is an extremely important set of skills to understand.
The best way to respond to a particular event? Initially, the best action to take is no action. Do your homework here. Do not react emotionally. Stay neutral. Seek wise council here. Evaluate all the different options and the possible outcomes of each. Challenge your current beliefs. Make a choice and live with the consequences, good or bad. Things are predictable. Read and read and read. Get mentally ahead of your spouse in the whole process ASAP, they are ahead right now.
As far as your spouse, until you have enough info to prove this wrong, assume there is another person (Hint: This is your first 180). Do not reveal anything about what you know and how you found out. "We both know that is a lie." is a great way to deal with any deception.
I wish everyone well during these difficult times. Remember that everything will be OK no matter what the WAS chooses.