If I remember correctly it's because he needs pretty much full time and specialized care due to medical issues, she does not. The retirement home she lives in cannot handle the level of care that he is at so he needs to go to that level of assisted living in order to, you know, keep living. She does not need that level of care, and the rooms aren't really designed for two. Think of it as - she needs a primary care physician and he needs the ER, you don't send someone to the ER for a physical and you don't send someone to a PCP for a gunshot wound.
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