To me its about a girl who broke up with a guy, and at the end she changed, in a sudden sense: "she killed the girl he thought he'd known". So she probably broke up with him for maybe a reason he thought wasn't 'her'. But the first parts of him being alone after her breaking up, he has a hard time, he's always thinking about her, he wonders if she ever thinks about him, and he just wants to know how she's doing. But as time goes on, he realizes that he wanted someone to be with him, but he still has time to find that heart. And for now he has to use this time in his life to get his feelings sorted and back on his feet, then he'll have more time.
To me its about a girl who broke up with a guy, and at the end she changed, in a sudden sense: "she killed the girl he thought he'd known". So she probably broke up with him for maybe a reason he thought wasn't 'her'. But the first parts of him being alone after her breaking up, he has a hard time, he's always thinking about her, he wonders if she ever thinks about him, and he just wants to know how she's doing. But as time goes on, he realizes that he wanted someone to be with him, but he still has time to find that heart. And for now he has to use this time in his life to get his feelings sorted and back on his feet, then he'll have more time.