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Tear Jerker: The Last Spartan
A rather small yet still powerful one occurs in Chapter 26, Garrus and Master Chief get into an argument over Tali almost finding out about Cortana. Garrus tries to pressure Chief into revealing Cortana to the crew, believing that they wouldn't rat him out because they practically revere the guy as a hero, while Chief continues to disagree. A intense argument between the two occurs that keeps building up and up until finally the Chief breaks his normal stoic attitude by practically yelling at Garrus, while almost preparing to hit the Turian. He then finally cracks open and mentioning all of his friends, practically the closest thing he had to a family are all dead. And all he has left is Cortana, and can't risk the Council taking her away.
John-117: She's all I've got left!
"I thought we were friends."
When trying to work together to restore Peak 15's VI, Tali angrily yells at Cortana about how synthetic lifeforms have made her people's life miserable, citing the fact that she'll never be able to experience normal life due to being stuck in a suit all the time. There's a pause before Cortana speaks.