MD,
When my son was thrown out by the girlfriend's mother he did stay out. I was really surprised as he had zero place to go (lied about all shelters being full) and was sleeping in the woods. He had called the police after girlfriend came after him with a knife and girlfriend was send to detox. I guess the mother was use to the situation as she went on a week long cruise. Good for her!!
Then my son was clear headed, talking about restarting his life, had passed a computer cert (while sleeping in the woods no less) and easy child friends in another town offered to help him start over. I sent $$$ and paid for tickets for him to move there, he was calling, optimistic about jobs etc., for about a month, then he told me he was going to work with a friend and would be traveling around.
Then the weird posts on FB started and the aggressive suicidal posts (which I completely think were posted to get girlfriend's attention) then he friended girlfriend on FB and I lost track of him for a month and he reappeared back where he had started from. When I finally did hear from him all he wanted was money and when I confronted him about being back with girlfriend he lied.
His last message was that I was the liar and I was the one harassing girlfriend. At that point, like you, I realized that all conversation, messages, whatever, were pointless, the only thing he wanted to hear from me is when I would send the money. It is so obvious when my difficult child has gone back to drugs and alcohol.
As difficult as it is, this will be over soon for your friend. We cannot understand staying some place that we are not wanted. They are not thinking clearly and it is heartbreaking to know that they can turn on us, but they can.
The only reason my difficult child left the home was he probably didn't now about the eviction laws. The puzzling part to me was from everything I had seen before he went no contact, the mother had let the girlfriend and him back into her home. As far as where he is now, I have no clue, as much as he and girlfriend fight, if they don't kill each other I can't see them staying together.
If I was your friend I would turn off the AC and lock it so they aren't comfortable, put as much as I could into someone's garage until they leave, and stop buying groceries, take as much as she can out of the home so they are not as comfortable as they appear to be.
I finally learned that I can not 'help' my son - so I have stopped - I just pray that one day he will call me from a treatment program.
This too will end!
(((hugs and blessings)))