It's even worse when he reveals his Tragic Keepsake—her necklace. Which means Spooner either saw her body in the morgue, or Sarah's remaining family members gave it to him at the funeral. Poor guy.
Even more crushing is the almost clinical way that Spooner recounts what happened to Sarah. Listen to his voice. He starts out so calm and factual that one can easily assume he's told this story before, most likely to Sarah's family and to the police after he recovered. Furthermore, he knew the exact percent that the robot calculated when it chose to save him over Sarah, meaning that Spooner probably demanded that the robot tell him why it didn't listen to him, which could only have broken him further. The way he gets choked up by the end of the story is really what seals it because he's clearly been repressing his feelings so hard that it causes the recurring nightmares and Susan's question brought it all rushing up to the surface.
Spooner: That was someone's baby. 11% is more than enough.
More tragic on that note—Spooner is someone's baby (his grandmother's) too, but the way he talks about it means he's clearly stopped considering himself as worth anything anymore.
Sonny finally admitting he was instructed by Lanning to kill him. He looks like he's on the verge of tears he cannot shed as he struggles to comprehend his own feelings about being asked to kill his beloved father figure. Spooner's sympathy makes it more poignant.