First of all (((justfriends))).
My experience is that no matter how long the lead in, the divorce process is still painful, and not something I could have well prepared for.
I found these books most helpful:
1. For good ideas on how to structure the divorce without ruining my life, his, or our childrens ---
Getting Divorced Without Ruining Your Life: A Reasoned, Practical Guide to the Legal, Emotional and Financial Ins and Outs of Negotiating a Divorce Settlement by Sam Margulies
2. For helping me to feel that I was not the only one going through some sort of "script", and that my now ex is not exactly abnormal, but in some sort of midlife "scripted" whatever that I no longer want to be part of ---
The Script: The 100% Absolutely Predictable Things Men Do When They Cheat
Elizabeth Landers (Author), Vicky Mainzer (Author)
3. And then... more recently, to help me recognize that yes, this really is traumatizing ---
Transcending Post-infidelity Stress Disorder (PISD): The Six Stages of Healing
Dennis C. Ortman (Author)