SJ - sorry you are hurting
As my father aged into late 70's he behavior changed rapidly and manifested itself in what became ever increasing bizzare ways.
If I had not seen this on a weekly basis and I called after a period of time, he may have said things to me that were hurtful but really not towards me.
In other words, there were dementia issues that started as anger, resentful type behavior.
Have no idea of this might be happening with your GF??
Wonder if you just said you like to stop in by yourself one day and take him to lunch to see what's up??
Don't know distance, but even if it's a days drive might bring you answers and peace??
Again, your in our thoughts here...
Peace