She broke up with him because she said it wasn't working out, and she had some doubts.
All these thoughts ran through his mind, then she asked him if he was fine.
He said "I'm okay" but that was a lie, what he really meant to say was "With you I'd die!"
SO that night he wrote her something on a piece of paper, and put it somewhere she would find it later.
In the morning she went there not expecting to see, her ex-boyfriend who had ceased to be.
She ran to his room and started screaming "Why!?". she opened a note with her name; inside it said "Without you I'd die!"