IB, Your first week has been a busy and fulfilling one for you, as well as openning the door for you to get a glimpse into the life of your xh. He's not living the happy go lucky life that you may have imagined. He doesn't have a clue about what he's lost...but in time...he will. He's just not to that cross road yet.
As for your son, I'm very sorry that the gf was so rude to him. No one asked her opinion about your son's behavior and how she would handle it. She's a therapist? She should have gotten the message from his silence at the beginning and should have stopped trying to engage your son in conversation when she didn't get any comments from him. She sounds like a doozy!
I'm glad you are doing well your first week. I believe you will enjoy your "empty nesting" time and will discover that there is life out there waiting for you to live. Spread your wings and fly! You've earned it!
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.