Is There a Silver Lining in This Personality Disorder Playbook?

A friend of mine, Chip, has the following qualities:  funny, witty, creative, smart, helpful, warm, generous,
and talkative.

Let's call these his ermine characteristics.

At other times he can be angry, very angry, irrational, arrogant, nasty, argumentative, rigid, and silent.  Let's call these his weasel characteristics.

The ermine is white in winter blending in with the snowy landscape.  When its fur turns brown in spring, it is called a weasel or stoat.  Same beast, different colourings.  They change to protect themselves from predators.  Perhaps Chip changes for the same reason.  I don't know.

In the 13 years that I have known Chip, from time to time, his weasel side would emerge.  He mostly stayed in when that happened, aware that he could be "moody" - his word.

When he's in a good mood, Ermine Chip refuses to talk about weasel behaviour and would immediately get weaselly when I try.  When he's in a bad mood, Weasel Chip does not seem self-reflective at all.  It is impossible to have a two-sided conversation with Weasel.  He does all the proclaiming, and whatever is going on is everyone else's fault.  Always.  In fact, even supportive, kind words said to Weasel are met with hostility.

Sometimes Weasel would take over so that Ermine went into exile for days and months.  Chip would seem to have a personality change and be almost unrecognizable.  During one of these times, I took Chip to a psychiatric facility.  They fed him and kept him for a week, eventually letting him out in much the same state he went in.  It took about a year, and the Chip I knew and loved gradually came back.

You may know people who somehow stumbled into adulthood with an undiagnosed mental illness.  They may be self-medicating with drugs or alcohol.  Having seen One Flew Over the Cuckoo's Nest, they fear and reject psychiatric help.  They are suffering, but won't acknowledge it.

When I ask Chip how I can help, he says, "Love me," but that's getting harder and harder to do.

Have you been in a situation like this?  What happened?