I'd say the other half in the breakup is doing well, or he would have wished her well in the song. Besides, he says "the best thing that happened to you is the best thing that happened to me" and "knowing you would have wanted it this way... stronger every day" says that she moved on before he did. I think this song is to reassure the other person that their relationship had as much meaning to him as it did to her, and that she should no longer worry about him because he's getting better.
I'd say the other half in the breakup is doing well, or he would have wished her well in the song. Besides, he says "the best thing that happened to you is the best thing that happened to me" and "knowing you would have wanted it this way... stronger every day" says that she moved on before he did. I think this song is to reassure the other person that their relationship had as much meaning to him as it did to her, and that she should no longer worry about him because he's getting better.