He destroyed himself with a single word.
At the time, he didn't know it. He didn't realize it would be his downfall.
It didn't happen yet. Not until much later. But it happened.
At the time, it saved him. That one word brought him back from the depths of despair. It gave him a reason to live his life again. It gave him a purpose. It let him move on.
He had to pick and chose who to save, all the time. It always killed him, every time. That time, he picked her. He destroyed himself with one word.