Why.

is my brother all of a sudden spending so much time with my sister? I don't get it. They used to fight all the time and she has told everyone that she doesn't want him around. And yet she is letting him come around.
It bugs me mainly because I had noticed my sister becoming more independent and doing more for herself after she was finally allowed to live on her own, but now after a few weeks of my brother spending alot more time there and dropping in on her unannounced often she has backslid and seems to be acting like she can't do anything for herself again. He seems to be undermining all that I and my sisters caretakers have been trying to do for months now.
I don't think he is doing it on purpose just that he has no idea what he is doing and it is making her dependent on him for things when she should be more dependent on herself. He treats her like she is incapable and a moron and she lets him because it means he will do things for her and she doesn't have to take care of herself as much.
She got used to being cared for by my mother and is spoiled and so she is letting him treat her like a baby so that she doesn't have to do things for herself.
This confuses me but mainly makes me sad.