GWN, Return his call Tuesday evening. Listen to what he has to say and then wish him luck on his surgery...nothing more. If he attempts to engage you into small talk about what you are doing or with whom, just cut the conversation short and tell him that you have someone at the door and hangup. The less he knows about what you are doing, the better. Let him stew.
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.