Shock
Obi-wan appeared normal. Outwardly, he had pushed aside the situation as was his habit and moved on, communicating with the others, discussing the future of the twins, the mother… himself. But inwardly, he was silent.
He didn't feel anything. Obi-wan knew that typically, the shock would have floored any other man. He shouldn't be able to function.
He wasn't.
The shock just hadn't reached him yet.
For now, he could put on the pretense of normalcy, the calmness that was expected of him. He would take Luke to safety, hide him from Vader's reach.
Then he could let himself cry.
