Personally I understand that in life... shit happens. That is why if a girlfriend of mine started letting herself go I would try and figure out what is weighing on her mental and emotional health that is causing her physical health to deteriorate as well.
Then try and help her and give her support. But I would only withstand being there for so long, till I just give up if I notice that she isn't even trying at all to help herself.
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I'd be at her bedside the morning going.