I wouldn't warn him. If you do, he will make it a point to avoid being available. He's a big boy and should be very much aware that a divorce is coming very quickly. Trust me, if the shoe was on the other foot, he would not warn you.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.
