You said he was in a car accident - did he receive a head injury? Brain injuries can cause massive personality changes and that could account for his odd behaviour. It could also be a mental health issue - you said he suffers from depression, could it be Bipolar Disorder or something? The problem is that because of his mood swings and failure to ackowledge a problem, it would be very difficult to get him to speak to a doctor or other qualified professional who could get to the bottom of things. I wish you all the best.