The ending is not what was emotionally touching for me. The ending was simply closure. The weepy moment came at the middlepoint, when SP went up in flames and I heard her scream. And in my subconcious mind I kept it that way. Sure, the game later told me she was alive, but here is my take on the ending:
After SP is gone, you feel lonely and get depressed. You start imagining getting more letters from her. And in the end you subconciously decide to burn up your own house. Right before the flames take you, you have a "Dream sequence" or "Out of body experience" And when the game ends as you journey up up up in the sky in the weather balloon, thinking of how SP is alive and well on the beach, you are actually burning up up up in the house.
EDIT: If you find that unlikely, consider this: You are playing the entire game from a first person perspective up until the house burns up. And in the ending part you play from a 3rd person perspective.