There's nothing wrong with staying in and reflecting, especially on days that are tough. No one but you has to know you stayed in. For all your W knows, you went out and had the time of your life.
This is the best time for self improvement. When you do stay in, read something positive. Make lists of things to improve on yourself, or clean the house, something positive for you. It will help with your PMA.
Sandi is a wealth of knowledge. Remember, everyone is different, and that while most things apply, some dont. The "believe none of what they say and half of what they do" is a guideline to follow which basically boils down to "at this point, don't trust them, and don't depend on them". Just because your W filed the divorce papers doesn't mean she's committed to the D. (Believe half of what they do.)
You're in the worst stage of this right now. Please trust me when I say it does get better.
You should focus on one thing...getting your mind to a place where you are going to be ok if this proceeds and you end up divorced. Remember, you don't want to be with this W. The old W is already gone.
I'm here for you buddy. I don't have all the answers, but I will listen and give you suggestions and support.