Although there's nothing in the song that specifically points to long-term depression (everyone feels lonely or unwanted sometimes), that's what I get from it. As in, the girl becomes depressed, and it changes her. She's not the same person that she used to be, and thus starts to feel like she doesn't belong anywhere. She's lonely, and everything seems hopeless. After being like that for so long, she's feels like she's "falling behind" and doesn't know how to feel better or get back on track. The "nobody's home" line could refer to her feeling like she has no one to go to for comfort or help.
Although there's nothing in the song that specifically points to long-term depression (everyone feels lonely or unwanted sometimes), that's what I get from it. As in, the girl becomes depressed, and it changes her. She's not the same person that she used to be, and thus starts to feel like she doesn't belong anywhere. She's lonely, and everything seems hopeless. After being like that for so long, she's feels like she's "falling behind" and doesn't know how to feel better or get back on track. The "nobody's home" line could refer to her feeling like she has no one to go to for comfort or help.