The answer

The partner

She thought about how these three words had taken ahold of her and turned her life around. But these weren't the only word with this effect. She would never forget the time that he had said three words to her that would have as much impact on her as the woman's did. And these same three words surprised the girl when she found herself saying them to him for the first time. And every single time after that it became more natural.
She did hand her life over to him one day and that same day she got his life instead. They were suddenly inseparable, the two lives had been intertwined and bound so close together that they brought a new life to the world altogether.
All by three words:
I love you
I can remember the first time I said that it had brought tears of joy to my eyes and as I said it for the last time these were replaced by those of a sadness I hadn't felt in a long time. So to finish my story I will sum it up by saying that the girl had once been me and today we mourn the death of my partner in life. The girl who had once tried to take her own life found herself handing it over to her soulmate only to discover that many years after mending her broken soul he found that he had given the girl his life and had received here in turn but he couldn't take it so he kept hers but took his back and ended it.