Depression is a state of low mood and aversion to activity that can affect a person's thoughts, behavior, feelings and physical well-being. It may include feelings of sadness, anxiety, emptiness, hopelessness, worthlessness, guilt, irritability, or restlessness. Two of the more common changes in emotion are anger and depression. Someone may have been a "hot-head" or an angry individual before their accident. I think you can visit to psychiatrists and psychologists otherwise depressed individuals are advised to talk to professionals is much better.
Every relationship is different, and it's difficult to give advice/suggestions about relationships when you don't know the person. However, I would say that all you can do is be there as a shoulder to cry on, a person to listen, and other than that, let it work itself out.