I think the song is about how he was there for the girl when she needed someone but in doing so he forgot about his own life. So now that things are going better for her, he's going to stick up for himself and saying "no reentry" into his heart. He admits that she makes him happy but now she's nothing more than a memory. He is saying he was there for her when she needed so what is so wrong with him that she can just leave him so easily. Then it gets angry saying she is alone in this world and that when she does finally find stability, it won't ever be beside him again
I think the song is about how he was there for the girl when she needed someone but in doing so he forgot about his own life. So now that things are going better for her, he's going to stick up for himself and saying "no reentry" into his heart. He admits that she makes him happy but now she's nothing more than a memory. He is saying he was there for her when she needed so what is so wrong with him that she can just leave him so easily. Then it gets angry saying she is alone in this world and that when she does finally find stability, it won't ever be beside him again