Celestia's death until the several chapters the Tear Jerker comes from the description from Twilights point of view, and accompanying music.
Pretty much the second half of chapter 44. When it's discovered that one of the foals injured during an attack on Ponyville is going to die a slow, painful death from manticore venom, the main cast have an extensive discussion/argument over whether euthanasia is an appropriate course of action.
Rainbow Dash believing the others betrayed, raped, and tortured her. The entire time she's telling the story she's crying throughout. And when Twilight overhears the details through eavesdropping, she'd crying as well.
Rarity's story of when she and Rainbow Dash first met. How do you not tear up over reading that?
What Applejack was experiencing in chapter 62 had to be forged from this stuff in the pits of hell itself. There's no other way to explain it.