Irena, I am so sorry. He does sound like he's in deep depression. And maybe bipolar. Maybe someone closer to his age can talk to him? If he got a new apt, that meant that at some point, he had to leave the old apt and go to an office and fill out paperwork, so at least he is capable of that.
He seems to need medication.
In the meantime, I'm sending hugs. Try to detach. If he won't let you, he won't let you. That's always the hardest part. We can see it but our kids can't.