I am so sorry that you are here but rest assured, this is THE best support group. Please read read read here and the articles in the healing library. Also post as much as you feel like. You are in the early stages and it is such a confusing time. The roller coaster's up and downs were the worst for me in the beginning.
I could have said a lot of what you shared in your post. It doesn't matter when he became "unhappy". Who isn't unhappy once in a while in their lives??? Your WS has extremely poor coping skills and boundaries and lacks courage and integrity. You offered him the GIFT of reconciliation and he turned it down.
If she is his subordinate, I'm sure this will get them in to a lot of trouble. Just saying.
Now you need to focus all your energy on YOU. Ok? Make sure you are drinking enough fluids, eating healthy, continue therapy, see your doctor if you are experiencing difficulty sleeping, depression, anxiety, etc. See an attorney so that you receive what you are entitled to. Focus on taking care of your needs, process all the shitty emotions that are happening so that you can heal and rebuild and move forward. You CAN do this!
P.S. I have a link below that you might want to check out.