Complex sentence: The story ends as he reads the final letter she had written to him a couple weeks before she jumped off a building to her death; one that would have made him realize how desperately she needed him to save her again.
Split into simpler sentences: The story ends as he reads the final letter she had written to him a couple weeks before she jumped off a building to her death. One that, had he gotten sooner, would have made him realize how desperately she needed him to save her again.