It seems like Ani is saying she has spent a lot of time pretending to be emotionally numb, showing that things don't bother her, etc. "Course numb is an old hat / old as my oldest memories" implies that this isn't a new thing, but more a thing she's been doing since she was young, a learned behavior. She hoped she wouldn't have to keep her emotions inside all the time when she got older and out on her own, but "any more pent up emotion / i think im gonna explode" - it hasn't happened. She continues to detach herself from her emotions and the world around her, but wishes it wasn't so.
It seems like Ani is saying she has spent a lot of time pretending to be emotionally numb, showing that things don't bother her, etc. "Course numb is an old hat / old as my oldest memories" implies that this isn't a new thing, but more a thing she's been doing since she was young, a learned behavior. She hoped she wouldn't have to keep her emotions inside all the time when she got older and out on her own, but "any more pent up emotion / i think im gonna explode" - it hasn't happened. She continues to detach herself from her emotions and the world around her, but wishes it wasn't so.